It's totally normal. I think it's teh body doing what the mind does by introducing all these thoughts in your head; I think it's just that initial reaction to being still which is so strange for many of us, especially early on.
Interesting anecdote: I just finished a play where I had to be dead on stage for about 40 minutes. I did get blackouts to readjust, but I still had to sit still--DEAD still for about 20 minutes or less a stretch. I would get those sensations, but no matter how much I wanted to, I couldn't reach up and scratch. Eventually, they go away. And the longer you're there meditating the less conscious you are of your physical body, until those don't happen at all.