Do you wear glasses? sometimes if the lens in them are not the right type they'll give headaches whenever you play... my sister had the problem (i dont need glasses
).. she had the wrong type of lens in them and it gave her headaches nearly str8 away within 10mins when using the PC..
Try turning the options like anti-anaslising and the texture filtering down...
Might work dunno but different refresh rates on monitors and games can effect people.