I used to have a housemate who would come in and watch me play Doom clones, seated behind my shoulder - she would get motion sickness even sitting that far away (in the 15" CRT days)
If I don't play for a few days I feel the same way when I am playing but I can power though that in about half an hour.
No surprise though since my flying career ended early when I couldn't hold my lunch, a (bumpy) hot humid day too much to eat and being nervous didn't end well.