Your body tries to compensate negative influence of fatigue, anxiety and depression. This require above normal energy deployment.
You can say that each of them may trigger any other.
E.g. You may feel depressed or having anxiety if you very tired. When it is difficult to do what was easy in past than your brain may go into depression . . .
Your energy is drain out if for any reason you are depressed, so your fatigue is increased. The same is with anxiety.
Anxiety can be related to both depression and /or fatigue.
Much more interesting is why you don’t have enough energy to compensate any of mentioned above problems.
It may be related to luck of proper diet, vitamin and/or mineral imbalance or another medical problem.
You may have hormonal imbalance if you in puberty or menopause stage.
Or maybe your problem has origin somewhere else.
In many cases in background is exposition to EMFs (electromagnetic fields).
More on that and related information are here.