I suffer from chronic sleep paralysis... which in of itself, is something to be fucking terrified of. For those who don't know what that is... when you go to sleep, your body locks up and stops you from thrashing around and moving, as it reacts to dreams. Your brain can't distinguish dream from reality when you're sleeping, so it only wants your body to act out what you're experiencing. The brain however has a failsafe in place that locks your body and keeps you relatively still, save for rolling over occasionally or adjusting for comfort in the night.
Anyways... with sleep paralysis, when you fall asleep (or mostly in my case) when you wake up, your body is locked into place, but you're still completely conscious. As your brain is also in a dream state, you tend to hallucinate as well. Luckily, my hallucinations are super rare and only tend to relate to the dream I'd already been happening. Sometimes my hallucinations are assholes, and I imagine myself waking up and getting up, only to realize I'm actually still in bed, lol. Some people aren't quite so lucky, and get floating spirits, dark figures and all kinds of creepy shit. It's also accompanied by a difficulty in breathing. You breathe like this when you sleep, and you're in no real danger, but when you don't know about it... the more relaxed, slower paced breathing is fucking terrifying, as you struggle to take deeper breaths to compensate for the scary situation you're in.
These episodes can last from a few seconds, to minutes. I'm pretty sure my longest episodes last about 5 minutes, so it's fucking shitty, lol. Sleep paralysis either ends with you waking up and being totally fine... maybe sometimes with a headache... or you just fall back to sleep and wake up later anyway.
Anyways, to get to the actual point... my greatest fear is that I won't wake up from it. I'll just be stuck in this terrifying state and I won't be able to escape it. There aren't any records of this actually happening to anyone, but you never know if you might be the first case, lol.