Though most people aren't likely to experience motion sickness from a 3D film, as many as 30 percent of the movie-going population suffers from a milder vision issue, causing side effects like headaches and eye strain. "The problem comes in with people who have 3D vision but have a weak fusional mechanism. Your eyes are having to work harder. The brain is sending extra impulses to keep the eyes in alignment," says a spokesman for the American Academy of Ophthalmology. When forcing your eyes to view 3D images for an extended period of time, viewers can start to feel eye strain, fatigue, or in extreme cases, motion sickness.
Conflicting messages to your brain add to your body's confusion. When you're watching an extremely realistic movie in 3D, but sitting still, your brain processes a false sense of movement. In sensitive viewers, this is leads to the nausea and headaches associated with motion sickness. If watching movies in 3D makes you queasy — but not queasy enough to give up your beloved flicks — an over-the-counter motion sickness medication should give you some relief.