Usually what gets my adrenaline pumping is when I calculate a line, and it's something like a really pretty tactic or mate... and I check a few variations, and it seems to work... that's when I start getting really anxious, OMG, OMG, am I going to finish this game in a really nice way?
Ok, calm down, double check everything... double check... calm down!
For whatever reason I can't remember getting nervous during my opponent's move, or when they reach for a piece, or when they make their move. Even if I spot a tactic I missed, and now my opponent can win material, I'm just calm for some reason.
Or lets say they've been pointing pieces at my king, then they suddenly play a sacrifice I wasn't expecting. I'm just like, ok, that's interesting, lets analyze.
Your opponent makes a move and you get that feeling. In a tournament! Has it happened to you?