I have this strange phenomena that happens whenever I have accumulated enough sleep debt, or am in a very relaxed state. Most recently it happened when I was exhausted enough to attempt Wild when first going to bed (I know what the concesus on doing this is, but trust me I had enough potential rebound built up and it was 5 hours past my typical bedtime 
). I was laying on my back and I had slipped in to stage 1 sleep completely. But what happens is I jerk awake fully alert, as if electrocuted. This time I remember my mind being completely clear, then a blank spot, and I a jolt went through me with a full second of panic.I felt typical SP in my extremities and lower body, but knowing this only helped calm me down as I recognize SP and generally enjoy it, So I’m not sure what causes this reaction to happen. It tends to only happen if I fall asleep on my back, but even then not all the time. The only time I’ve used a binaural aid this happened to me, several times within the hour. Anybody have any idea what it could be?
That was my former conclusion, but it doesn’t seem very typical for them to startle you awake, right? I’ve compared them to the ones other people have while sleeping, they don’t usually seem to practically convulse when they happen. Maybe they’re just really strong ones?
If I’m thinking about what you are talking about, i have these. I don’t have them very often but it feels almost as if you are falling and the bed, or whatever your are sleeping on, catches you. For me, I think it is that I am having a light dream that I don’t really remember but still feel a bit of the physical part of it…so pretty much it’s like the kick from inception, u feel like you’re falling so you wake up. Opposed to the hypnic jerks, this would explain the short panic you have after waking.
They can be really strong. I have sometimes thought that my bed was collapsing, that I was slipping on ice, etc. Also, when somebody else is sleeping next to you, their hypnic jerks can really feel like convulsions. I usually get two kinds of disturbances while falling asleep: a mild, electricity-like “wave” and those strong jerks that can make me fully awake.