During exercise, the brain releases endorphins into the bloodstream. Along similar lines is the theory that exercise increases the release of brain monoamines. Low levels of brain monoamines are associated with mood disorders such as depression. If exercise increases the amount of brain monoamines, the person's mood will improve as well. After a difficult day, many people like to enjoy a long, hot shower or a warm bath to relax.
Exercise produces a similar feeling.
As always, if worries and stress persist and interfere with daily life, seek help with a professional counsellor. Make sure that you organize time for an aerobic workout about three times a week. This could involve a bike ride, aerobic class, or just plain running. When running, try to land on your heel and push off your toe to minimize strain on your knees. Get good shoes.