Do symptoms like slow heart rate go away quickly?

Depends on cause: Slow heart rate is sign or physical finding. It's normal during sleep and periods of tranquility and rest. It often causes no symptoms or, if severe, may cause abnormal fatigue, lightheadedness, or even passing out. Very slow heart rate (under 40 beats a minute) if present during wakefulness may be pathological. Normal hearts increase rate promptly with exercise or stress of any type.