Or it may be the sign of a too hectic schedule. Some fatigue in life is to be expected. But if you experience a marked change in your energy level or your fatigue persists despite adequate rest, see your doctor. Being tired all the time may be a sign of an underlying medical problem. If you're burning the candle at both ends, you're going to feel it.
Anxiety can also cause fatigue.
If worries are keeping you from relaxing, you're likely not getting the rest you need. You may not go to bed early enough. Or, more likely, you go to bed but can't sleep well. With age, it becomes harder to get uninterrupted sleep. You sleep less soundly.