I just started taking aikido, and I've noticed one thing: No matter how tired I am during the day, I'm always very energetic as soon as I walk through the doors of the dojo, I'm immediately more energetic and happier as well. And the feeling seems to last for at least a few hours after I leave as well. Did this happen to anybody else when they first started? Any explanation for this? I mentioned it to Sensei and all he did was nod knowingly and say "I know."