Todzo I feel your plight! I had suffered from brain fog for quite some time. It had gotten so bad that I was having difficulties in remembering friend's names, when we last met, and what we last talked about. I even found myself running up and down my apartment's stairs to check and ensure that I had truly locked the door, among other annoying situations.
I started taking Neuro Boost Piracetam, about 3 months ago, and noticed a slight increase in memory about a month into taking it. A basic bit of information regarding Piracetam is that it is a derivative cyclic of GABA and works by stimulating the Acetylcholine receptors which are implicated in thought and memory functions. I've been taking around 2,400-4,800mg a day for the entire time, and as I said I've noticed a steady slight increase in my memory. It isn't anything similar to some "super-duper you're awesomely smart now" drug, but it has helped promote my memory and overall cognitive functionality. I've been taking Piracetam alongside L-theanine and Choline Bitartrate. L-Theanine stimulates the GABA and is reported to have anti-anxiety benefits. Choline Bitartrate is a acetylcholine neurotransmitter source, which I use to replace the transmitters used by Piracetam due to its stimulation ACh receptors.
Other drugs and vitamins I've found to be beneficial in improving my memory have been: Omega-3 fish oils, ALCAR, and Alpha-GPC. If you aren't taking a mutlivitamin and some Omega-3 fish oil I'd suggest you go ahead and give them a shot as that can already help you out both in physical and mental health.
I know getting a good rest is also key in not having brain fog. So sometimes it just isn't going to be avoidable with Sleep Apnea, although using some supplements, vitamins, and drugs can certainly make these days easier and less cumbersome than usual.
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I hope you found any part of this beneficial, I know how bad it sucks to live with brain fog, and I hope you find some help or relief from it soon!