###Human: Why am I feeling excessively fatigue or sleepy with low heart rate? ###Assistant: Hi. Yes, daytime sleepiness occurs due to sleep apnea. If it is present in its severe obstructive form, it can cause a host of cardiac diseases like atrial fibrillation, coronary artery disease, and heart failure. The exercise intolerance initially develops the consequence of early heart failure. Also at your age, you may be suffering from chronotropic incompetence, that is, the inability to increase heart rate with exercise, and regular graded exercise will help you. Stay off from alcohol and cannabis.