Overview: Fatigue is a feeling of tiredness or lack of energy, even when sleeping enough.
Feeling tired is common. It happens to all of us. We work too hard or exercise too hard. But fatigue is a feeling of tiredness or lack of energy even when you are sleeping enough and when it can't be attributed to heavy exercise or work. It is not at all the same as feeling sleepy. If you are fatigued, you may also be sleepy, but sleeping won't make you feel less fatigued.
People who are fatigued feel as if they have no energy or motivation. This may sound like depression. The two can be related - fatigue can certainly be depressing! But fatigue isn't primarily a mental health problem.