I didn't have the brain fog until recently, and it got so overwhelming that I couldn't think at all, only feel. In my case it seemed to totally coincide with panic/anxiety/stress. It came on in spells which I'm not getting anymore. I felt like I had lost my humanity or had a lobotomy or something, and I got worried that I might be gradually turning into a human vegetable... which only made the anxiety worse. My brain temporarily became like that of a baby, complete with babylike crying etc. I think there's no way that was due to the apnea alone, though the CPAP may have encouraged hyperventilation which contributed to the anxiety which helped fuel the whole mess. I have something more than sleep apnea going on which is yet to be conclusively diagnosed. But the current theory from my neuropsychiatrist is that I have an autoimmune disorder triggered by strep which is causing ongoing neurological damage, and which may even have caused or contributed to the apnea. He says he's seen hundreds of cases similar to mine.
Actually a lot of your symptoms sound very similar to what I've been going through. Descreased sex drive, migraines, chronic sinusitis, deviated septum, nearly passing out while playing sports, tinnitis, auditory hyperacusis, doctors thinking it's all in your head.
Doctors are only beginning to recognize how widespread autoimmune problems really are. It's possible that like me, you have apnea, and then some. Treatment of apnea can result in improvements in many parts of your life. So I'd say get treated for apnea if you have it, then work through the rest of the issues if they don't resolve with better sleep.
In my case, nearly passing out during sports was likely due to just being really out of shape, cardiovascular-wise... even though I'm in pretty adequate physical shape otherwise. My lazy exercise habits have resulted in strength but no endurance.
Don't be afraid to see a knowledgeable psychiatrist, as they will often be the ones to validate your suspicion that yes there is something physically wrong with you. Again I'm seeing a neuropsychiatrist who turned out to be the first doctor with a clue about my non-apnea physiological symptoms. Think of it this way... if all your doctors are drawing a blank, wouldn't you like to have a psychiatrist draw a blank too? Just get a smart one.
I assume you know about limiting caffeine to mornings only, and getting at least some modest exercise, taking a daily multivitamin and avoiding diet soda, junk food or anything with preservatives; so here are some lesser-known tricks I've found that might really help you with sleep regulation:
Watch your melatonin cycles! In other words, get plenty of light, preferably natural daylight, during the day. In the evening, keep artificial lighting fairly dim, and have it be incandescant if possible. If you're reading a book obviously make sure you have enough light to read, but keep it soft and gentle. Evening is for relaxing. Light is how your brain knows whether it is day or night, and that is essential to the regulation of your sleep. Even staring at a computer screen can mess up your melatonin. So dim your monitor in the evening way down so that it feels gentle on your eyes.
If you ever wake up at night and have to use the bathroom, do it in the dark as much as possible. Use the dimmest nightlight that allows you to navigate and function. If you turn on the overhead light in the bathroom when you get up at night, even if it's dimmed, that can still be enough to reset your brain's melatonin cycle and then you probably won't get any more really deep sleep that night.
On another wavelength, many people (including me) are convinced that even nominal exposure to ambient electromagnetic fields (EMF) can disrupt biological processes, especially the melatonin cycle. If you minimize your exposure to EMF, especially in your bed where you sleep, that can actually make a difference. It's a controversial subject, but apparently some people are quite sensitive and the types and strengths of EMF can vary dramatically even within the same room. I got a Trifield Meter on eBay and used it to locate all the sources of EMF in my house, and I was able to fix the worst ones and avoid most of the others.
The worst was a water pipe running under my bed. A clamp-on ammeter revealed that this pipe had 2 to 4 amps on it at any given time! This is not supposed to happen but the fact is, it happens all over the country. Some neighbor with bad wiring is pumping current into the water main, and follows the pipe into your house seeking your neutral as a path back to the power company's transformer up on the pole. Other times it comes in from the grid seeking your ground. This is really insidious!
My water line current was causing an EMF density of 6-10 milligauss in my bed! To give you an idea, 2 milligauss or higher is generally believed to cause biological effects. But the actual threshold of subtle influence could be much lower. In Russia, they try to keep it below .1 milligauss and there is not anywhere in my house where the EMF is that low. I "fixed" the water line current, breaking the circuit by installing a dielectric union near the water meter, and driving a seperate earth ground near the electric service panel. That made a HUGE difference, and now my bedroom is down to only .4 milligauss. My wife and I both noticed an immediate improvement in sleep. It's a real phenomenon, I'm convinced of it.
There's an excellent book called
Silencing The Fields written by Edward Leeper, a physicist with literally decades of experience in locating and reducing EMF in homes and businesses. There may be some useful web sites out there (as well as some crackpot ones), but this book is BY FAR the best resource on practical EMF reduction that I've found. Definitely worth the money. It is filled, cover-to-cover with practical information and case examples. One rarely encounters a book like that.
Best regards,
-Ruggy