I take 25mg of Toprol XL daily for mitral valve prolapse. I don't have high bp. Is fatigue a common side effect with such a small dose? I have been on this dosage for about 4 years, but I feel tired during the day sometimes. I recently took up running and am a very active person who enjoys running several times a week. My resting heart rate is 48 bpm. Also, what is the best time of day to take this med? I have always taken it during the morning because my doc said it would control the chest pains better.