Sounds to me like you may have had altitude sickness from Base Camp. I am surprised there were not doctors to check you out. Almost 6,000 meters or over 18,000 feet is a serious challenge on a concussed brain. Dr Dorothy Gronwal studied the effects of just 8,000 feet on concussed brains and the challenges were substantially evident.

For aircraft, FAA regulations requiring supplemental oxygen when flying above 12,500 feet for more than 30 minutes or any time above 14,000 feet.

I don't know if it will help but HBOT pushes oxygen into the cells and helps with capillary growth. HBOT, Hyperbaric Oxygen Therapy

The concussed brain appears to struggle to use oxygen efficiently.