Got exposed to lot of natural gas over a 3 month period. (Long story) Eventually figured out that my blood begin clotting like crazy. I have factor 5, so I was predisposed to it, but I was having 2-3 TIAs a week for a couple of years. Huge cognitive decline.

Only when a large clot showed up in lungs did they figure out what was going on.

Week after being on blood thinners and simple programming problems that were taking me weeks to solve were back down to minutes.