beloved friends, I come to you in an hour of great need and beseech you. please help me

why do I get such horrible FPS in some games? I get 90 FPS in boneworks, superhot, stride, and I never feel any sickness when I play these games. When I play fallout vr or skyrim vr even without mods or no mans sky and a few other games then I get 45 fps and I get a horrible headache within 10 minutes of playing.