You're up. You're down. And you're soon up again. It seems like you spend your days riding an emotional roller coaster. Are these changes normal? The answer is "maybe" -- so long as they don't disrupt your life or the lives of people around you. Many things can affect how your mood shifts throughout the day. For example, because of body rhythms, most people feel upbeat and energetic around noon but tend to have more negative feelings during the early afternoon or evening. Sometimes, mood swings are a symptom of a mental illness Or they could be a clue that something else is happening in your body. Serious mood shifts that threaten your well-being can be treated by medical professionals. Lifestyle changes can often help mild ones. But first, you'll need to figure out what could be causing your bumpy ride. Stress and Anxiety Day-to-day hassles and unexpected surprises -- both the good kind and the unpleasant ones -- can definitely chang...