Runner's High

I think I'm hitting the running enough to start getting a runner's high. It's leaving me feeling energetic  after my run. I typically use the treadmill (it's damn cold outside here in Minnesota, USA) and vary my speed anywhere from 5.5 mph (8.9 kph) to 7 mph (11.2 kph) and try to put at least 25 minutes in. Sometimes 20 minutes if lifting after.