Exercise releases pleasure hormones. You'll feel great even on minimal amounts of any types of physical activity, from yoga and deep breathing to running and football, and any vigorous exercise can leave you feeling happy and exhilarated after even a short time. But to experience what is known as an aerobic high, where the brain is awash in feel-good endorphins, studies indicate that you must do intense exercise for an extended period. If you've reached this point, you could suddenly feel as if you're running on air and exerting no effort at all. If you're fit enough to do so, consider pushing yourself to reach this high.