Unfortunately fatigue is a factor in depression that is often to to lack of REM sleep
The important neurotransmitters Serotonin and Dopamine and also depleted because of the neurochemistry imbalance cause by lack of REM sleep , digestive issues and it is a bit of a vicious cycle.

I found eating a natural fooed diet, medication and a strong mindset to get better by exercise and meditation. I know that this is not easy when you are depressed having 2 bouts of very serious depression myself

Chris