I do the same thing! My brain gets overwhelmed by the feeling of “OMG, THIS BOOK IS AWESOME” and I have to take a little break to cool it down. In my case, it looks like me turning the book over in my lap and taking a few deep breaths, though sometimes I have to get up and walk around, too.
Laughter; there are plenty of books that are funny, but laughing out loud while reading is a rare and much appreciated thing.