What is that startle reflex that makes you jump or twitch awake?

I think you’re referring to the “hypnic jerk” reflex. This happens during the transition from wakefulness to sleep, aka hypnagogia. Since the a typical night’s sleep cycles through around four periods of light wakefulness, there are several such transitions. The hypnic jerk reflex seems to be related to stress.

Many times I notice it happens when I start to drift off at the same time a mini dream kicks in where there might be some content in that little clip that would make me flinch, like, if I felt I was falling or something like that. I can never remember much of those dreams anyway so I’ll never get to the bottom of it all.

House called it a myoclonic jerk.

@Simone_De_Beauvoir

I see what you did there.

@woodcutter lol

It has also been suggested that it is triggered by your brain thinking the body is dying (very much similar to actual death when the body jolts). Interesting question though…I get aural and visual jolts as well, quite regularly, which are supposed to be rare. They appear like hallucinations but very fast. They are very vivid too, which is just plain odd.

edit: I also get a buzzing feeling in my head but I am on various medications that could be responsible for this as well!