Funny you should say that, this happened to me again the other day.. seems to happen when i've got too much on and I'm struggling to deal with it - it's like i'm shivering just under my scalp. is that the same for you?

I've been ignoring it - figure i should either stop smoking or stop drinking coffee and get some real sleep! But, I don't know why it happens.

Keep asking your doctor though, it might be a sign of something..