I truly believe that exercise helps me keep my optimism on life. The current challenges of a business partnership going south and the resulting stress associated with it may have me in a bad place if I did not exercise consistently. I did not look forward to waking up early and going to the gym or the exercise itself, but I definitely felt much better afterwards.
It is that time out of my mind, working my muscles that always helps bring me around to better possibilities for the future. If you are feeling stressed by current conditions or situations that do not seem to have a good outcome looking forward then I recommend some type of exercise (it really does not matter what kind, just along as you move your body). Some people believe that with exercise your blood flow is slightly shifted away from the brain and out to working muscles, therefore you are not able to dwell on negative thoughts for too long. Combined with an increase in endorphins and you have a recipe for positivity.
While the studies on reduced blood flow to the brain with exercise are a little limited, there are significant studies to back the release of endorphins. I do know that I feel better and tend to fair better with exercise than without. Please take care of yourself.