Yes, I would assume you get energetic in a fight because you may get a sudden rush of adrenaline which can help you be distracted from the pain your body might be receiving, but once the adrenaline wears off you'll be in a whole world of pain depending on how hard you got hit or if you even got it at all.
It's probably better if you go into a fight energetic because of one, the adrenaline, and two, your body is getting you prepared by making you jumpy while you're most likely mentally preparing yourself for whats about to happen.
