They call it lock-in. When you have motor neurone disease (MND), you get locked into your own body because this condition doesn't affect your mental acuity, your sharpness of thinking or your memory. It's maddening. It doesn't dull your senses, so you can still feel pain like anybody else. If you were to stand on my foot, I would feel you standing on it, but I wouldn't be able to do anything about it.

It starts in different places for everybody. For me, it was in my feet – within a couple of days, I couldn't move my toes. On Christmas Eve 2007, I had an MRI scan which was absolutely clear, and that ruled out all of the easy things such as a trapped nerve. The consultant told me that, given my family had a history of MND (my father and grandfather both died of it), it was highly likely I had it.

I met my wife Louise at art college. We got married in 2004 and our son, Oscar, was born on 25 August 2007. So this was his first Christmas, and we didn't want to mar it. The whole family realised it was likely to be bad news, but because it hadn't been absolutely confirmed I think we all held out hope. It was only at the end of the following January that they ruled out all of those complicated but fixable things.

With MND, messages from the brain fail to reach your motor nerves. It crept up my body so I gradually lost the use of everything. When I lost the use of my legs, we had to get a hoist to help me stand. I was wheeled from room to room in this hoist and the same day we got it, Oscar pulled himself up on the bars of his playpen. When I first had to use a bottle to pee in, he started using his potty. When I got my wheelchair, he started using his walker.

There was always a good chance I would contract MND. I was 22 in 1996 when my dad died, and I was very aware of it from that point. With my dad and granddad it took six months from the onset of symptoms to death, without any kind of treatment. I was prescribed the only drug known to have any effect, riluzole. It's meant to delay the progression by three to six months or so. But when it starts to progress, it progresses quickly. Now, I've just got the use of my lower jaw and my eye muscles. I can't move my neck any more – speech and breathing are the only controls I have.

I wear patches for pain relief and I take pain relief tablets every day. If I didn't, I would feel all the aches and pains of muscles as they slowly stop working and shrink, joints that become unsupportive, my pelvis starting to flatten, the ventilator hose wrapping around my head. Occasionally, I've had pain from my hips to my knees, down the side of my thighs. I felt like the skin had been ripped off my thighs, my feet had been dipped in boiling water and my fingers had been dipped in ice.

When every aspect of your life is shredded, you have to try to find pleasure somehow, in order to make each day possible and move on to the next. You can't cry, because every time you get upset your nose runs, you can't breathe properly and the ventilator gets full of saliva and mucus so it's difficult to swallow. If you get frustrated or angry, you can't move to lash out, or shout. There's nothing you can do about it.

The biggest frustration for me is that if there's something that needs to be done, I can describe it so clearly but then people do something else. It's infuriating. You can learn to accept that you can't do things for yourself, but that doesn't belie the fact that you know you could do them better. Louise calms me. She and I practise reiki, which helps me relax. It takes me to a very deep, calm place sometimes. Then there are treats like taking a bath. When I'm in the hospice for respite care, the bath is one of the only places where we get to be completely alone.

Before we got married and had Oscar, we had a discussion about whether we should do either of those things. But the chances of me getting cancer or having a stroke or being hit by a bus were higher, so why should we hold back? People sometimes ask why we had a child when we knew he could get MND – I feel the same way about that as I feel about me getting it. It's really bad luck, but the chances of something else happening are far greater.

I certainly don't regret my 34 years on this planet and I hope MND is a problem that will be treatable and fixable one day. A new centre in Sheffield has just got planning permission. It's going to open when Oscar is about three and a half [the centre opened in 2010]. That's 30 years of research to crack it before he's my age.

I don't think about dying as much as you might expect. It's not at the centre of my thoughts. It's secondary to making sure my family and friends are as prepared for it as they can be, by talking to them and being with them. I'm also making a memory box for Oscar to give him a sense of me. In it, there's my favourite leather jacket, which his mother hates, there are photographs of me, the original Jungle Book LP my dad bought me when I was a kid, a brass turtle I used to play with, the watch my mother gave me when Oscar was born. Things that define and describe me without shoving anything down his throat.

Stephen Hawking has had this disease for 20 years – it's a unique, unexplainable phenomenon. But I wouldn't want to put my family and friends through this for the next 20 years. I want to see my boy grow up, but I don't want to watch someone else doing the things I should be doing. It was so difficult watching him take his first steps, holding someone else's hands.

Interview by Anne Wollenberg

• I Am Breathing will be released on 21 June, MND Global Awareness Day. You can set up your own screening and raise money and awareness for MND through iambreathing.com