Easiest way I know is to do some physical activity. make yourself physically tired.
Problem with that right now (paging flagamuffin too) is that I have this going on which means I've gone from running 3x a week to 0, and I also don't have a gym membership at home. Guess I could do core workouts but those don't do as much for me (and are incredibly boring).
Running indoors is fine if and only if it's on a track. I really dislike treadmills and all of their ilk. Running outdoors beats everything else. Maybe it's a winter thing for me too, could be new shoes or the fact that I'm running more frequently. Either way, it's not fun. Why do you kinda hate gyms?
Well the ones I have most experience with our crowded college gyms. Thirty different kinds of weight equipment, all designed to work one single muscle cluster, all incomprehensible. Lots of people, very few of them doing anything constructive. Six square inches to do pushups. Loud and odd-smelling.