This Is Disconcerting

I seem to get headaches when I knit for too long. A very scary thought, actually. Maybe the repetition of it, or staring at the same color for a long period of time does a number on my head and it objects.

This is disappointing because I have to stop every once in a while even when I really want to keep going. Should I keep knitting and ignore the headache, or should I stop knitting and let my head rest? Such a delimma...