When I get an autograph (celebrity, sports player, etc) ... I keep my physical cool, most of the time ... but my head releases some kind of adrenaline / nervous endorphin. The bigger the "star" (to me, of course), the more blitzed out I get. It takes a good 15 minutes for me to rest.
The worst I've ever gotten was when I was chilling with an music artist in a hotel room.
It's like the scene in A Christmas Story where the kid meets Santa and says "football".