I am one of the thousands of people afflicted with sleep paralysis. Most nights my sleep is undisturbed. I lay down, dream, and wake up. Night after night. But sometimes when I wake up I can’t move. I dread those times.

It always happens the same way. My bedroom door opens in my dreams and a dark figure watches me from the doorway. The fear is so intense, and I can’t move. My limbs feel like they’re made of lead. I struggle, I fight, I try to cry out for help. My heart beats, rushing through me as I struggle to move. And that figure keeps staring at me, hating me.

And then, like I had broken the cobwebs that bound me, I could move and spring up. My bedroom door will be closed, the dark figure will be gone, and the fear will bleed off me. But I can always feel it lurking. I can’t go right back to sleep or I’ll slip back into the paralysis.

I can never predict when it will strike, but I can often recognize the signs in my dreams when an attack, for lack of the proper word, comes upon me. My bedroom door opening. If that happens in my dreams, I wake up before my body paralyzes.

So if you’ve never heard of sleep paralysis, it is a little understood condition. While either falling or sleep or waking up, a person can get locked into complete muscle atonia and often have terrifying nightmares of intruders in their rooms accompanying their complete helplessness. Some attribute this to demonic activity, and after experiencing it, I can understand why. When I’m in the grip of the paralysis, and the dark figure is watching me, nothing has ever frightened me more.

The ‘intruder’ as the figure is called in medical literature, is thought to be caused by a hyper-vigilant reaction in the brain caused by finding yourself unable to move while you’re still not fully awake and causing your dreams to react accordingly. It is thought that sleep paralysis is responsible for tales of succubus, incubus, demons, UFO abduction, out-of-body experiences, and host of other, similar tales.

Science still doesn’t fully understand the causes of sleep paralysis and there are numerous theories explaining it. Luckily, it doesn’t threaten your physical health, just your sanity. Something I try and focus on when I’m in the grips of it as I lie they’re helpless. But it’s hard to remember that the figure isn’t really there.

Last year, after a particularly bad incident, I wrote a poem about it. All day the figure had haunted me and writing down my fears went a long way in shaking off the experience.