HBOT is an expensive process with usually little gain. Some see no gain, others see a small gain. Either way, it usually requires 40 to 80 sessions (dives) to see a difference. One could easily spend $10,000 on HBOT. It can be shown to improve capillary growth and function but daily living functions are harder to measure.

You can effect your B-12 and D3 levels with supplements. 5000 units of D3 and 2500 mcgs or more of B-12 methycobalamin would be a good start. I read a study years ago that connected low cholesterol to poor brain function. Larges doses of Omega 3 DHA fish oil may be worthwhile.