Not a Doc, but I have heard of some cases which may have similar roots.
If he's tired, but supposedly getting 'enough' sleep, then sleep quality may be an issue. There's a condition (don't know the medical term) where a person 'almost-wakes-up' several times a night (as often as every few minutes in the worst cases). It's not going to full alertness, but it's enough to bump them out of the REM stage, which is when the actual rest and recharge happens. Usually the cause is a breathing problem, I think tonsils or something in the sinuses. Very sketchy, I know, but it's all I know about it.
Also, low iron levels in the blood can cause fatigue - does he eat enough meat, or get vitamin supplements?