The last time it happened, I remember trying to scream but no sound came out of my mouth. I knew I had my phone near me, so I grabbed it and started dialling for help. But when I looked down at my hand, I realised I hadn't called anyone. I was awake, yet paralysed and still dreaming. It was as though my body and brain had been completely severed from each other. While I was imprisoned in my mind, my body had been cast adrift.
Sleep paralysis is the most terrifying thing about narcolepsy, so I am lucky that it doesn't happen to me that often. With the exception of sleepwalkers, most people's bodies become paralysed when they enter REM (rapid eye movement) sleep. This is the stage of sleep where we dream and this paralysis stops us getting up from our beds and acting out our dreams. But I can wake up during this stage of sleep, and when I do I am completely paralysed. My eyes are open, I can look around me but my brain has not come out of REM so I cannot tell whether what I am doing is real, or part of a dream.
I was diagnosed in July this year. I had already been at the sleep clinic in Guy's & St Thomas' Hospital in London for 24 hours, electrodes attached to my body as they ran test after test. Finally, the doctor told me I had narcolepsy. This is defined as daytime sleepiness: the inability to stay awake despite a normal, full night's sleep. But daytime sleepiness sounds like quite a gentle, cosy disorder. It isn't; it feels like a curse. I am 27 years old and I have slept for at least 15 hours a day, every day, for the past 13 years.
It is horrible to look back on life only to see how much I have missed because I was asleep. But now past experiences have started to make a lot more sense. My mum stopped me from going to sleepovers and parties when I was a child. They would make me so exhausted that I had to take Mondays and Tuesdays off because I was too tired to get up. At school I took lunchtime naps.
Sleep will creep up and envelop me within a matter of minutes. I try to fight it, but sometimes I just can't. My work as a neuroscience researcher at London's Goldsmiths University means I often attend conferences and seminars. It does not look good to doze off halfway through a lecture, but sometimes there is nothing I can do.
I can fall asleep anywhere. I remember waiting for a delayed flight at an airport with an old boyfriend. The place was packed, everyone was shouting. Despite sitting on a hard, marble backless seat I was asleep, still upright, in seconds. "How do you do it?" he marvelled.
I first went to the doctor when I was 14, but no one took me seriously. I was told it was hypersomnia, the opposite of insomnia, and sent on my way. Two years later, I was taking cocaine to help me stay awake. My drug habit didn't get me high, it simply helped me get up in the morning. I have always needed a boost and recently an old university friend reminded me how much I would dose up on ProPlus before a night out, just to make sure I would stay awake. I visited various doctors over the years but was always fobbed off. It was my age, my student lifestyle, an underactive thyroid gland, anaemia ... none of them was right and I grew more frustrated with myself. Why was I so lazy? What was my problem?
Battling to stay awake in the face of overwhelming tiredness is such a familiar, horrible feeling but I have developed little tricks over the years to keep it hidden. At a desk or in a seminar I try to fall asleep with my hand holding a pen so it looks as though I am pretending to write, but I am not sure how convincing that is. To stay alert I dose up on caffeine, underdress (so I will be cold), pinch my thighs or wiggle my toes - anything to keep me moving. The more uncomfortable I can make myself, the better chance I have of staying awake, so I avoid comfy chairs and warm places for the same reason.
Narcolepsy is like being plucked out of the world only to be dropped back in it, hours later. I am constantly trying to catch up with my life. One day I went missing. When no one could reach me it was my best friend who concluded that they would find me somewhere in a park, asleep. No one believed her, but she was convinced and, sure enough, that is what happened. I had been asleep for hours only to wake and discover countless missed calls on my phone.
Thirteen years after the first doctor's appointment, I finally know that narcolepsy is the reason for all the holes in my life and I can at last have the support and treatment I need. Rather than people thinking me rude for dozing off in front of them, I can explain myself, which is a huge relief. But while receiving the diagnosis was a momentous occasion, there was no drama sitting in the clinic talking to the doctor. I was just trying to understand what this meant for the rest of my life.
I soon started to feel angry, though. If only someone had listened to me I would not have spent every day of so many years battling on my own. I could have lived a more normal life.
The drug I have been prescribed, modafinil, has made life easier. It gives me palpitations and I have lost my appetite, but now I cannot physically fall asleep - which is good, except I have to inhabit a no-man's land for most of the day where I am awake and tired. But it has only been three months and things are improving as the medicine kicks in a little more.
Mornings are still challenging, even with the drugs. It can take up to an hour before I am ready to go. For years, I have relied on an elaborate system of alarm clocks. Two clocks are set to go off within five minutes of each other. This is followed by a third, set on a five-minute snooze cycle for half an hour, then the iPod kicks in and finally the TV comes on. This always comes on last, when I am almost awake, to avoid me dreaming the programme instead of waking up to it. I have put a lot of thought into this system: on days with an early start, I will set the TV to come on twice.
My sleep disorder is the result of reduced levels of the hormone, hypocretin, which controls wakefulness. For most people, sleep comprises non-rapid eye movement (NREM) followed by REM, when you dream. With low hypocretin, I go straight in and out of REM sleep. This sharp shift between wakefulness and dreaming makes for some strange symptoms, such as hypnagogic hallucinations, which I have had all my life and find quite pleasant.
I start seeing shapes move before my eyes, sometimes accompanied by sounds, and it tells me that I am about to sleep. I use this to my advantage. I am still awake, so I know that I must be falling asleep the moment I see them. It is a useful early-warning system.
The more relaxed I am, the more real the hallucinations become. I remember having a massage and looking at a man sitting across the room drinking water. It seemed to make sense until I realised I could not possibly be watching a man in a restaurant drinking water while I was lying face down on a massage table. I managed to bring myself back into wakefulness again by telling myself that it was not normal and could not be happening.
As a way of helping me realise when I am asleep and when I am really awake, I have started learning how to dream lucidly. A lucid dream is when you can control what you are doing while dreaming. Imagine you are looking at a bus. Now look away, then look back. If you were dreaming, instead of seeing the bus again, you would see something else - a tree, a giraffe, a spaceship. I try to do this sort of test to see where I am - in a dream or in reality. Once I have done that, I know whether to wake up.
In a strange way, it is good that I got my diagnosis later in life. Instead of having an excuse - I've got narcolepsy - I have had to push myself. But now I know what is wrong, I know life is going to get easier. And I am looking forward to it
• Helen is a pseudonymn. This article originally appeared under the subject's real name. She was talking to Catherine Jones.
