sometimes i think it's a bug near me, or sometimes it's a shadow. i'm not usually conscious enough to turn on the light or anything rational, but i am conscious enough to sort of realize that it's not real while still feeling completely terrified (if i think it's a bug, sometimes i'll swat at it. i think.). i usually sit up in bed (i think) and spend the 30 seconds (or however long it lasts) confused and scared and trying to figure out WHAT THE HELL IS HAPPENING. it's like that feeling you sometimes get when you wake up and can't remember what day it is and spend a few seconds trying to clear your head. i'm pretty sure it's not real, but i don't know what it is and i can't seem to do anything about it. then i'll just immediately fall back asleep as if nothing happened.
we were talking about this today at lunch, and i think i've figured out that it might be (or at least related to) sleep paralysis?
...the paralysis may be accompanied by terrifying hallucinations (hypnopompic or hypnagogic) and an acute sense of danger. Sleep paralysis is particularly frightening to the individual because of the vividness of such hallucinations. The hallucinatory element to sleep paralysis makes it even more likely that someone will interpret the experience as a dream, since completely fanciful or dream-like objects may appear in the room alongside one's normal vision.
i'll usually wake up just fine the next morning and won't remember the episode until later in the day, and that's when i get a huge case of the heebie jeebies and think PLEASE DON'T EVER DO THAT EVER AGAIN EVER EVER EVER OH GODDDDDD.