Headcanon: Cortisol spike right before you wake up. Brain goes, "something must have alarmed me", and cooks up phenomena: loud noise, feeling of falling/tripping, etc.
About the second thing, I have felt something similar. Especially the part about it originating around the collar bone and neck. It's probably something like a nerve misfiring. I sometimes think it's weird that the body doesn't misbehave more often than it does, it's an enormously complex system after all.
Possibly. Or a pinched nerve.
I don't think it is a cosmic ray, or it wouldn't always occur in the same part of the body. ;0)
>I sometimes think it's weird that the body doesn't misbehave more often than it does
Indeed.