Sometimes happens to me for now got controlled drinking lots of water and taking zinc and few iron supplements.
Discussion
What a bummer specially since you seem to like FPS games. Do that happen more often with older FPS like Doom ?
Again doesn't affects me at all is probably some thing around the frames in some games lol but can play normally fps
Do you by any chance have motion sickness with Chromatic aberration? I had a friend like that, I once got even a dev of a game to add an option to disable it after I sent them feedback. This option is a demon for some people.