There is nothing in the world like a good workout to help you focus, put things in perspective, and relax.
When I was a kid, I wasn't a superstar athlete. I wasn't even a very good athlete. I played sports, but I was merely "competent", not good. But I loved to be active. I could ride my bike all day long. I loved taking long walks by myself or with my friends. I could swim for hours. My favorite childhood memories are of time spent outdoors, biking up to the tennis courts a half mile away from my house or playing baseball in the street or biking to the pool a mile away and swimming all afternoon.
I've carried this with me into adulthood, to the point where my mental and emotional health are intricately tied to how much physical activity I'm getting. If I go more than 2 days without physical activity---at the very least, a yoga session and/or a half-hour walk---I get cranky, I can't concentrate on anything, and I'm generally miserable. I think I go through a sort of withdrawal. A few months ago, I had to quit working out for several weeks for health reasons (no yoga, even), and I was completely miserable. My body and mind actually craved it.
I work out almost every day. Whether I'm happy, sad, angry, upset, confused, exhausted....no matter what I'm feeling, I still work out. My favorite workouts are the solitary ones, where it's me all alone, pushing myself. Running is my favorite (although for health reasons, I haven't been able to run in a very long time), but swimming does much the same. Lifting weights is especially cathartic---it's me against the weight, seeing how far I can push myself, how much I can lift, how much can I draw from inside myself to get just one more rep. Yoga is a more recent obsession---I like the quietness it brings, the fact that it doesn't require pushing, yet calls you to draw on your inner self, on reserves you didn't know you had. With all of these activities, I often enter a meditative state---the repetition, the solitude, I guess put me there.
Working out has gotten me through every rough period in my life---finishing my dissertation, my early career struggles, bad teaching days, the deaths of my grandparents. When I get upset, I head to the gym or head out for a walk. I often joke that my sneakers are my therapists.....but for me, there's some truth to that.