One day in the summer of 2004, I lost my memory. I woke up in hospital surrounded by my husband and four children and I did not recognise a single one of them. They were strangers. I am told there was some build-up, in that I had been off work for a few days with a gastro-intestinal upset and became quite confused. My daughter tells me I called my husband Stephanie. They were told by the hospital that I had viral encephalitis, a serious neurological infection affecting the brain. I was 43.

The first person I recognised was our youngest son, Leo, who was 11 at the time. I had been in hospital for five and a half weeks, initially in a coma, and he spoke to me from behind the bed. I was unable to see him there, so it was his voice I recognised, and I said his name. It was my first meaningful word for such a long time and they were all so delighted and relieved. And it was so special that it was him that I recognised. But, sadly, that recognition was only fleeting and when I was discharged six weeks later, arriving home was like crash landing into someone else's life.

I had to believe that my husband was the right person, but I had no sense of certainty about him. With our children, I had a bit more feeling of security because, although I did not recognise any of them, I had a feeling that they were ours. It was, I suppose, a strong maternal instinct. But I had no sense of belonging to this family who, I was told, were mine. I remember feeling completely separate from this group of individuals who seemed so intense and confident together. They were very clearly a unit, but one that I didn't feel part of. And I was very scared.

I didn't recognise our home, so I couldn't find my way around. I even had to be helped to go to the right rooms. My younger daughter, Georgia, who was nine, left pink heart-shaped notes all round the house: "Bedroom", "This way to the bathroom", and "I love you, Mummy". It was a lovely thing to do and I've kept those notes, but at the time I struggled to believe this was the home I lived in. I remember, in particular, not wanting to wear any of the clothes I was told belonged to me. I simply denied they were mine – a lot were lost and many have never been found. My husband thinks I disposed of most of the items that were previously my favourites, ones he supposes that I identified with the "me" I had lost.

In my life prior to the illness, I had a good education and 27 years of experience nursing in the NHS. Now I found myself unable to name plants and animals, as well as not knowing where to go two doors from home. I had always wanted to be a mum and was the person who organised family life – the cooking, the driving and so on – but now I found myself completely misunderstanding the needs of my own children. Struan, then 16, and Helen, then 14, would say (as they still do): "You know I don't like spicy chicken!" and "Why give me sugar in my tea when you know I don't have any?", but I really don't know that.

I want so much to get it right, but without the most basic memories I spend a lot of time getting it wrong. They have a mum who doesn't know them individually and who doesn't remember how to be Mum. At times, it has made me feel like a dismal failure – and it has been very difficult for them.

But things are not all doom and gloom. The children – now aged 22, 20, 17 and 15 – are fun-loving in a full-on way, and they tease me to try to make me laugh. It's part of the way this family communicates. In the years following my illness, I didn't recognise this and so it upset me. But more and more these days, I am able to understand the repeated teasing for what it is – just fun – and react more normally.

I've also learned how helpful it can be to write things down. It started with reminders on scraps of paper, such as how to use the washing machine and clean my teeth (I had forgotten these things too) and later developed to things such as "Helen dislikes kedgeree" and "Leo enjoys football". With the passage of time, and with the help of my written reminders, there have even been moments when I've been able to feel like Mum again – I mean, the mum I'm told I used to be – making smiley-face crumpets or driving my children somewhere they really like going. That feels good.

I've met others through the Encephalitis Society who suffer from the effects of this illness, and that is another thing that helps. Often people say "I know how you must feel", but like so many dramatic experiences in life, only those who have experienced it can really know.

Best of all, over time, I have pieced back together some memories. The first and the strongest were of my own childhood – a walk in the park as a child near where we used to live in Sheffield, for example, or a family day out in the Peak District to see the dams. I was able to link these memories to the people who I was told are my mother and father, as well as my three sisters. I started to feel a sense of belonging with them. The feeling was wonderful – something I will never take for granted again. My parents were so happy – it meant we were a true family unit again.

Later, I began to get a few memories of my first years of meeting Ed too, although these are far more vague. But I have no recollection at all of the children being born, being young or growing up. I feel so lucky with my husband – not everyone would love their partner a second time round if they met them again from scratch years later, which is essentially what has happened to us. It's great to feel totally confident in our shared love. I feel very sad for him, though because I am now not like the person he married. I feel bad about our social life together too. I am not very good at seeing our best friends – the people we have known as far back as the 1970s. They still think that once they give me a hug and say, "Claire, I'm Pete!" that everything will come flooding back. It doesn't, and consequently, although I can still relax and enjoy a joke, I find socialising easier with new friends who have no expectations connected to the "old" me.

Making things even harder is the fact that I can forget any of them all over again within minutes because I have ongoing problems with facial recognition. It happens with my own family. I can usually recognise my husband or children at home if they are the only ones there, but there are occasions when I muddle Ed and Struan and they have to give me a gentle reminder. One time, Helen knocked on the door and I asked how I could help her. "It's me, Mum!" she laughed. When I'm out of the house, I struggle to pick my husband and children out at all – unless I can remember exactly what they are wearing – so I always make a mental note of it as we go out. I get little grins, waves and special eye contact to help me feel confident that it's them.

Maybe all this has affected them less than I think. I do see a lot of happiness in them. All four are confident and independent and have a special bond. I was talking to Struan, now 22, about things the other day, saying that I see my life as a jigsaw, one that has fallen off the top shelf and smashed into many loose pieces. He thought for a moment, and said he felt we'd found the corners now. He said happily that half the fun, the whole fun really, should be building the edges and then putting the pieces back in the middle. The only thing he did say can be frustrating for them is seeing me work so hard to live up to a preconception of what a mum should be. He says it can make me fuss a bit too much, which sometimes makes him and his siblings snap back.

Last Christmas, Georgia, 15, said, "You are no longer the integral cog in the family Christmas machine." She was only joking, but I feel that mums should know their children's life stories. It's part of the fabric of family life. I hardly know anything about my own life and almost nothing about theirs. Much of the time, I am still a stranger in my own world – a bit like an actor in the wrong play.

That said, over the last six years since this all happened, I have had a fantastic amount of help, both professionally and from my family. I may not be the wife, the mum, the nurse, the friend that I believe I was before. I may not be able to bear the thought of watching old home videos or seeing old photographs that remind me of the 20 years I've lost. But how lucky I am to be able to say that my heart is in the right place, even if my head isn't.

Claire Robertson was talking to Kate Hilpern

www.encephalitis.info; Tel: 01653 699599

Ed's story: 'We no longer have the shared history other couples do'

Because I'm a doctor, while Claire was in a coma I was well aware of the possibilities for recovery or otherwise. Then when she woke up it wasn't so bad because right from the outset she did improve a little each day. I'm an optimist, so I remained hopeful that this would carry on.

It did become clear that she would have lasting problems, but there was never any point where we – the children and I – thought, we can't cope with this. Also, Claire helped us hugely by being very strong. She gave us a lot of hope herself and as time has gone by I think I've been proved right in my original feeling that things would improve.

Obviously it was peculiar at times in the beginning, first because there were times when she would remember who I was and then times when she had no recollection of me at all. We've built up mechanisms to deal with it – I wear a necklace with a shark's tooth on it and that's her visual cue that it's me if she gets confused.

There's no word or particular definition for this, but one of the major problems she had was this thing of not believing in the concept of herself, being uncertain of her own identity, as well as of everyone around her. It's hard to explain, but in the same way that she didn't believe her clothes were hers or had difficulty accepting the house we lived in, I think she may have had the same feelings about us.

She still often says that she feels like an outsider, but to us she is the same.She looks the same, and many of the things that were true about her before the illness are still true now. She still has traits we instantly recognise: her drive to do things, a need to be busy and her sense of humour are all still the same. All those are things that haven't changed, and that's a lot of things. She has lost those experiences she had in the last 30 years, the memories.

There has been an element of starting again in terms of our relationship as a couple. We don't have that shared history that other couples have. All the reference points have gone. Nowadays, we do have the things that have happened in the past five or six years as a "new" history and although she still has trouble with those memories, they are stronger.

It has changed her character, but then it's changed the character of all of us. Our eldest daughter has said to me that it has benefited her in a way, helped her grow up. It's helped all of the children become self-sufficient.

The hardest part in the beginning was when she came home and was terribly emotionally unstable, which was so out of character for her. She was crying a lot and very anxious, and there really was nothing I could do for her. That was a terrible time.

The other thing which has been hard has been her inability to understand sarcasm. It sounds like nothing, but we have always been a family who use that kind of humour. So she took everything we said literally and to her it sounded like we were being very horrible to each other. That upset her. But in the end it's impossible to change that kind of behaviour – nobody can live their life literally. In the end we just used to shout "Tease!" every time she looked doubtful or worried about what we were saying.

It has been hard for the children, and as a family we've lost something, that maternal thing of remembering the little bits of history, the specifics that I'm rubbish at – though I do just about remember all their birthdays.

Right from the start I took the view that the priority, the people who needed most protection – emotionally and practically – were the children, not Claire or me. We sat and talked about it. I had no qualms about telling them everything, but at the same time you put a positive spin on things: "This has happened but we'll get through it, things will get better." I asked them if they wanted people to come in and look after them, to be with them in the house, but they all decided they wanted to cope on their own. I think that was beneficial and I think it mostly paid off. They are very confident and have probably come out of it not too badly – we still have a very loud house.

Ed was talking to Steve Chamberlain