I suppose it depends on the type of practice or where I'm at in my training. When I first started, I suppose I had the feeling you described... but I think it had more to do with the fantasy I had of being one step closer to becoming an invincible fighting machine.

Now-a-days, that "energy" comes from the discovery of things I *thought* I knew. When that happens, I'll want to keep training, talk after class, try it out on the wife when I get home... However, I think that renewed energy or sense of well-being can come from anything you enjoy doing, whether that be martial-arts, sports or gardening.
I can't remember the last time I left the dojo in a bad mood.
Where in Florida did you train?