I found this (your) post on another thread and copy/pasted it here on a new thread to find/help you, if possible ... I hope you don't mind. Perhaps you have found the cause of your problems, I don't know. However, having had so much success with my machine, it is a shame to hear of your CFS, etc. (I can relate to trying to walk without sleep too, along with lack of cognitive function and headaches).
I also have similar symptoms despite treatment with cpap for OSA. Please let me know if you find out anything regarding your symptoms. It seems there are a million things that can go wrong with the body, and most of them cause fatigue. However, doctors don't understand the difference between being tired and not being able to walk b/c of it. So, hopefully somebody will be able to figure this out for you.
I also had OSA but have been free of it for several months (sudden weight loss, and not by any lifestyle change or choice of my own, illness, unfortunately ... several things are going on in this body; mass confusion) anyway, the weight loss made my need for my CPAP obsolete ... at least for the time being. First, the pressure was at 13, then to 8, then to 3, now to no CPAP. The weight loss has stopped but I'm still really tired because I have poor thyroid function (Hashimoto's Disease) and we can't get it under control. And some kind of white matter brain disease called Leukoencephalopathy, some demyelination, and swollen lymph nodes on both sides of neck are of most concern ... but are throughout my body -- all "non-specific" for cause(s) or diagnosis at this time ... so I dangle in waiting.
Just in case it may be your machine, settings, or equipment ... I'm going to post some questions; if your problem has been remedied or found to be caused by something else not relative, but causative, feel free to just ignore this post/thread. I assure you, I will have no hard feelings if that is the case and do realize my post may be a waste of your time.
Does your headgear fit properly?
When was your last sleep study conducted?
Do you use nasal pillows or nasal mask (these cover the nose only), or do you use a full-face mask (covers nose and mouth)?
If your gear only covers your nose, is it possible your mouth could be opening during sleep?
Does your machine have a humidifier on it?
Do you have oxygen hooked up to your machine as well?
Is your machine equipped with C-flex or similar, so the pressure is not too much when you exhale while sleeping?
Do you "wrestle" to get comfortable with the machine and/or gear?
Do you feel that the hose is long enough?
Are you cleaning your machine as the manufacturer recommends and changing your filters?
Perhaps you need a different machine, I've seen that posted several times as well with requests for information about particular machines/masks/hoses/remedies ... I posted the link on another thread, where I found your post (above).
It used to be a great site and the people on the OSA board were very knowledgeable. Of course, that was some years ago ... so the more/most "knowledgeable and experienced ones" that I know of may no longer be of such significant number; it's worth a try though, perhaps the new group is even better!
My problem was with the nasal sleep gear; my mouth kept opening during sleep and I didn't know it ... so I had to switch to a full-face mask to cover both my nose and mouth. If you are using nasal gear (mask or pillows) and your mouth does not stay closed, you are not getting any benefit at all from your CPAP. Another option is to try a chin strap; I couldn't handle that though, I tried it ... it was very uncomfortable for me. This gear is a very individual thing and each person has to make his/her own personal "tweaks & adjustments" to suit. There used to be a lot of advice in there about comfort.
I found a way to "train" my mouth to remain closed and not fall open, a lady in that forum posted it. I did so and the open mouth problem was solved. When I was absolutely certain that the problem was solved, I switched to the Swift Nasal Pillows and I absolutely love that gear! Once I got used to my machine, my nasal pillows, and had the pressure corrected ... it was nothing to put that thing on and go to sleep; I actually looked forward to it ... finally, I was getting great, quality, productive sleep.