Maybe little things are getting to you lately and you find you’re often in a bad mood for no particular reason—this shift can be a sign that you’re on the verge of burnout. Exhausted minds and bodies are susceptible to sour moods and have trouble bouncing back from small setbacks. If you’re training hard and often and find that you’re a bit down or short-tempered, you might need to take a few days off from working out.