Some people have the experience of not being able to function because of a persistent sense of fatigue. This could be from the moment they wake till they go to bed.
Some common symptons

Foggy head .Not able to focus and concentrate.Not able to organize their lives
Easily fatigued after little exertion
Not wanting to get out of bed in the mornings
Excessive sleeping during the day
Use of drugs, energy drinks colanuts , coffee etc to excess

There are many different causes for this and it is interesting to explore a few

Many of these symptoms are experienced by people who have had a viral infection e.g COVID and can last months or years after the infection has gone

It can happen with depression or even ADHD . A very common cause is STRESS
Do you snore, or have difficulty breathing whilst asleep? That can be a big contributor as you may not be getting quality sleep
Also anaemia if your blood is low in Hemoglobin from poor diet , excessive bleeding etc
There are many other conditions that can cause fatigue but it is not a nice feeling as it can make your life unpleasant and hopeless
TIREDNESS CAN BE MENTAL= no will or motivation , apathy. That could be a sign of depression
BUT

There is always hope