An all around tired, even exhausted feeling is a common complaint among travelers as they are often on a limited schedule with too many things to see and do and too few hours to sleep. The best thing you can do is rest. Lack of sleep, too much time in the heat and sun, not enough to eat or drink or acquiring an illness are common causes of fatigue and are best treated with some rest. When planning your day, leave time for meals and a little siesta.