For thousands of people, a proper friendship is a distant dream. Unseen, unheard, forced to live in perpetual twilight, the only friendships they can form are anything but 'conventional'; and for many years, I was one of them. I developed ME in 1997, after contracting first tonsillitis and later a glandular virus. At barely 11, I was too ill for school, with a host of confusing symptoms.

I was endlessly exhausted and suffered terrible headaches. My ears were so painful that I couldn't lie on my side. I slept well into the afternoon and was wide awake all night. My arms and hands were often too weak to even hold a pen, and I completely lost my appetite.

The early years of illness remain a blur to me, but the one aspect that is still vivid in my memory is the loneliness. All day, every day, I lay in bed, which may sound like heaven to many, but it slowly took its toll, weakening my body and mind. I could not cope with visitors, even if I didn't see them - just the knowledge that there was someone in the house (other than my parents) was too exhausting to contemplate.

After many months of staring at the walls of my bedroom, I somehow gained enough strength to return to school. From then until the age of 15, I attended part-time as regularly as I could manage. It was at this point, when the pressure of GCSEs really began in earnest, that my health took a fateful nosedive.

I deteriorated rapidly, and had no choice but to leave school without a single qualification, having been too ill to take any exams. I was unable to walk, and had to crawl on all fours to get from one room to the other; I had awful dizziness; tiredness confined me mainly to the sofa; and I was gripped by such horrendous nausea that just the thought of food sent me reeling.

I lost touch with my friends, with whom I now had nothing in common. Illness was the only thing I knew: as my peers completed school and went on to college, my weight plummeted to five stone, just two months short of my 16th birthday. I was hospitalised and tube-fed, while the consultants informed me and my parents that I was close to death from severe malnutrition and multiple organ failure. I was treated as an anorexic.

After nine weeks I left hospital. After that, the only thing that appeared to concern my medical team was whether I had lost or gained weight. The ME was pushed to one side. Soon I was left entirely alone, and again I dipped dangerously low. The only people who could really appreciate what I was going through were those who had been through it themselves. Over the years of isolation, I had developed a network of 'ME friends', largely through online forums, and these friendships formed the centre of my world.

For the next four years of my life, I was housebound, spending the majority of the time in my bedroom. My curtains remained closed all day to keep out the daylight; I was too ill to read, watch television or hold a pen - any sound had to be quiet, and any activity (such as my mum reading a page or two of a book to me) could last no more than a few minutes; the pain was in my muscles and all through my head; my hands and feet were icily cold; the amount of food I could eat in one go could fit easily into an egg cup; and I was so sensitive to smell that even plain water was too strong to bear. It was an achingly lonely period of my life, punctuated only by the letters and cards sent by friends, none of whom had ever met me, yet all of whom understood exactly how I felt, without ever having to be told.

I first met Lynn Gilderdale in an online blogging community. To me, and all her other online friends, she was known simply as Jessie. She struck me immediately as an incredibly thoughtful and expressive person, with the strongest will I had ever encountered. The horrors she described to me, about her past as well as the unending misery of her day-to-day life, affected me more than I can ever put into words. I wondered at her endurance.

At the time I was still severely affected by ME. I could read, write, type and look at the computer screen only for very short periods of time (and frequently not at all). Any exertion, however small, left me dizzy, shaky and in dreadful pain.

I could relate to a lot of what Lynn told me: the course her illness had taken, the way she had been treated by the sceptics of this world - such as disbelieving doctors - and the nasogastric tube-feeding. There may have been a nine-year age gap between us (when we first met I was 19 and she was 28), but she was so much like a sister to me that our ages never mattered.

"Em, hope you don't mind me saying so ... but it seems to me that you and I sadly appear to have had quite a few similar (nasty) experiences with regards to our ME ... Had you noticed that? I feel sad that other people have suffered like me, and I'm sorry that you're one of them. It's just SO wrong."

"You and I appear to have battled through a lot of similar horrors in our ME pasts, which means I know how painful they must have been for you, too ... and I'd give anything for you to not have experienced those horrendous things as well. The only "good" thing I can glean from the fact that we've both had such similar bad experiences ... is that it means we can understand each other perfectly, only having to explain the bare minimum before we seem to instinctively understand where the other one is coming from."

Hearing about her own suffering, and seeing through her diary entries how she dealt with everything that came her way, inevitably led me to re-evaluate my own situation. I had never known anyone who, in the face of so much pain and sadness, exuded so much hope. She refused to give up, even as one problem after another came crashing down on her. Her courage and unshakeable willpower would reduce me to tears.

"You are one of the most beautiful people I know, and you deserve only the best; if I could give you anything to make your life easier I would. Hugs and heaps of love and comfort are on their way through the air to you, and I hope they can help you even a little bit. Be strong, and keep in mind that one day this nightmare will end."

Because Lynn could not talk at all, her only form of expression was through typing. She was so articulate, and had a natural ability to put a huge amount of feeling into every word she wrote. Receiving a text or email from Lynn never failed to make my day. They were often so long, chatty and heartfelt that she had to type them out over days.

I promised Lynn that one day I would make the journey to visit her, but we lived 100 miles apart and we were both too ill to travel.

"I feel such a strong bond with you ... I've felt drawn to you right from when we first "met", and as I get to know you more and more I see the reason I was/am drawn to you is very simple ... you're an AMAZING person and a complete STAR. No arguments ;) I'd dearly love to meet you one day - health permitting on both sides, obviously. You never know though, it *could* happen one day ... right? (I've probably just scared you into leaving the country now, haven't I?!)"

We shared a love of crafting, and doted on our pets. She once sent me a beautiful Easter card that she had painstakingly made herself, and I sent her a handmade birthday card for her 30th. We sent each other photographs on our phones.

Lynn was my first port of call when I needed to talk. I knew she would immediately understand how I felt, and she was always there to lend support, commiseration or join in with my occasional joys. She would text me when she was feeling down, or had something she wanted to get off her chest. She often spent many insufferable weeks in hospital, but managed to sneak her mobile in with her, and we would text each other every few days. Despite being in tremendous pain and permanently exhausted, she could still make me giggle. We could be utterly daft with each other and feel totally comfortable about it.

As the years passed, I had the bittersweet experience of finding my health gradually improving, while Lynn's deteriorated. I felt so guilty that I was ever so slowly getting my life back, yet she - who deserved nothing less than a happy, pain-free life - was not. I spoke to her about it, afraid she would be upset at my progress, but although I knew she must have been feeling so much sadness, she was so wonderfully, genuinely happy for me.

"Been meaning to text you to say "YAY!" at your new OU student "status", so ...YAAAAYYY!!! I'm so proud of you, and I hope you get as much out of it (and more) as you expect to."

"I know that you still feel like absolute crap on a daily basis, but you've done so well and improved so much this year, and it's been wonderful to read your obvious joy at (re)discovering new things ... how could I forget your excitement at going to a certain supermarket for the first time in years?! I've loved to read about you meeting new people and going new places, and I hope with all my heart that this next year of your life is the year ... the year all your dreams come true and you recover. You deserve it so much."

Knowing how passionate Lynn was about raising awareness of the horrors of living with ME, I asked her one day if she would be prepared to help me with an article I was writing. She was all too willing to do whatever she could, so, with patience and great care, she answered several questions, which I could then use as the basis for my piece.

Yet she never saw the finished article.

I was ill with a flu bug when the news about Lynn's death broke. Sensing from (somewhat cryptic) comments online that something was terribly wrong, I clicked through to the news pages. The moment I read the headline, my head began to spin, and seconds later I was crumpled on my bedroom floor, crying my heart out. It couldn't be true.

I had never lost anyone so close to me before, and had no idea how to cope. Lynn had been a part of my life for what felt like my whole lifetime, and I could not bear the idea that she was gone. We had always spoken of ESP, and sending love and thoughts through the airwaves to each other; but that could no longer be. I grieved for her.

In the year since she died, Lynn has helped me in more ways than I could have thought possible. I travelled to her funeral, which was the longest journey I had undertaken in more than 10 years. There I had the privilege of meeting her parents, and I was able to say goodbye to my dear friend. It will forever pain me to think that I could never make the journey to visit her while she was alive.

There have been many times over the last year when I have wanted to send her a text. I lost my beloved dog, whom Lynn knew was so important to me, and I lost my grandad. She would have been celebrating with me about my progress at university, and I would have sent her heaps of photos of my new puppies, because I know how much she adored animals.

She could never quite understand what an impact she made on the lives of everyone who knew her, and would never have dreamed of the devastation she left behind.

My friendship with Lynn changed my life. It may sound like a cliché, but she helped me realise just how precious life really is. Her tenderness touched my heart, and she did something very few people had done before: she believed in me.