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.

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.