It typically doesn't last too long (depends on how long you were exposed to high altitudes for?). If its been 4 years, I'd suggest its something else that manifests as similar symptoms which you might want to get checked out.
After a month at altitude in the Alps this summer I never seemed to recover. I went to see the doctor after two months and was diagnosed with Lymes disease which I must of picked up from a tick bite in the Cairngorms before I left. Get yourself checked out is my advice.