I had the 'hit by a bus' fatigue feeling continuously! for quite some years.
slept 12-18hrs per 24- and still never felt awake-guess it was chronic fatigue (poss c f syndrome) - but yeahhhh! somehow got rid of it/ or it just disappeared some years ago- now it only hits me v v v occasionally but yep sometimes 'without any reason'- (the hit by a bus pain happens far more frequently, but usually a lot milder than it used to)
things I'd changed:
most important- what hannah said ! - pace pace and pace again- building up activity levels that slowly that you actually dont notice the building up- you need the patience of an ox...(is that the right animal?)
better sleep hygiene- like no normal cuppa in eve, chamomile (or other non stimulating herbal) tea instead,
do some muscle relaxation in bed
a memory foam mattress! (if I sleep anywhere hardish- 'hit by bus pain' goes nuts!!!- air mattresses however arent too bad)
trying to do some body and mind 'exercises' every day- so that you actually are 'tired'- but again too much of either, too much of any kind of stimulation... and I'm like 'on speed' and cant stop even if I hurt like a dog already- and consequences CAN (but strangely dont always) last for days/weeks...
and doing too little- also raises pain levels and I think can increase tiredness
it's a v v v v v v v v v v v v v difficult balancing act!
and of course... the c f might have just 'run its course' and all I tried to help myself might have done diddly