Still not sure what methylation is........sorry if I'm being dense.....
Watch the Methylation Made Easy video #1 linked in my signature, but basically what Beyond said. Your body takes folate and B12 and uses it to make methyl groups. This runs over 40 very important processes in the body, including DNA, neurotransmitters, detoxification, and so forth.
If your methylation is running poorly, then you will have a wide range of symptoms, which explains the symptoms of ME/CFS.
So, for example, you're having problems with sleep. Sleep is regulated by the neurotransmitters serotonin and melatonin. If you're not methylating properly, you won't be making very many neurotransmitters, therefore, you won't be sleeping very well.
If you improve methylation, you will make more serotonin and melatonin, and therefore be able to sleep better.
Same deal with the GABA/glutamate balance - it should go back into balance, so you're not wired and tired.
I've had success with all of those by doing methylation treatment, and don't need to supplement for those directly any more with 5htp, melatonin or GABA.