Laughing after workouts.

It happened again today. I was cooling down after my workout (100 squats, 100 lunges and 100 burpees), sweating so much it was dripping off me and I was actually sliding across the mat but I was laughing so hard (and loud) that I wouldn't have been able to stand anyway. The last time it happened my wife came upstairs to see if I was OK. Smarter people than me could explain it in terms of endorphins and Brain-Derived Neurotrophic Factors but sometimes working out is just so much fun!