Now, if I am feeling down, I go for a run. I usually start feeling better almost as I head out the door -- in part, I believe, because I am taking charge and doing something. But by mile four, I can actually feel my thinking beginning to change, from negative to positive, as if four miles, or about 30 minutes, is some kind of threshold. On longer runs, by about mile 13 or 14, I start to feel a mild euphoria. If I run faster, I'll notice it earlier. If I'm doing an easier, slower run, it takes a bit longer. On really long runs, of 18 to 20 miles or more, the nature of my thoughts go beyond just positive to creative. I start having brainstorms, one after the other, and I begin to feel "one with things," for lack of a better way to describe it. It's like deep meditation in which your personal boundaries open up and you no longer notice where you end and everything else begins. - www.washingtonpost.com