It sounds a lot like chronic fatigue syndrome. My husband developed it after an accident and injuries. It usually starts with illness or injury. His has been around for a long time now. Hopefully it won’t be for these people.
The best thing we’ve found to help you is eating healthy! We have a whole society that says, I know the way I eat isn’t healthy and I’m surprised when they get unhealthy! And would rather take drugs than fix them. 🙁