I'll mention something related, just to see how widespread my experience is. Sometimes when I am just about to fall asleep, I suddenly become very aware of my receding consciousness. It's a strongly uncomfortable feeling accompanied by a rush of energy that wakes me up instantly.
It feels almost like my body thinks it's about to die, so it does a desperate hail mary to stay alive, or something. Very unsettling.
I have always mentally separated what I described in my first comment from what I have come to associate with the term hypnic jerk.
The first is more of a mental, physically still thing. The other is, for me, a sudden motion of a large body part, usually linked to dreaming about falling off something. More importantly, the latter is emotionally neutral. I wake up going "oh, I didn't really fall. It was just a dream."
When the former happens, it is very emotionally uncomfortable. It's a feeling of pure dread, but sort of wrapped in cotton.
Yes I have this sometimes. It's even accompanied with a sort of tingling in/on my head that starts from the back/crown of my head. I always realize it's happening when I start to lose track of what I was thinking about, and can't recall thoughts I had just before I realized that I was falling asleep.
By this time it's too late to just let it happen, and I'll have wasted a 'chance' to fall asleep so to speak.
It feels almost like my body thinks it's about to die, so it does a desperate hail mary to stay alive, or something. Very unsettling.
Does anyone know what this might be about?