Guys, it's a combination of factors. I got it when playing COD4 at a LAN and started getting it often after that and slowly dissected the experience to come to a solution. Do all these things when you feel the symptoms coming on:
Firstly, it started after I got my 26" monitor and I noticed it happened when I would lean in and it captures most of my peripheral vision, when I would lean back it would ease; so lean back comfortably and relaxedly.
Secondly, it happens when changing views rapidly and reducing how fast you look around in the games, ie, how fast you change the scene, either by dropping your mouse sensitivity, looking left and right slower, or just by slowing down yourself, will ease it.
Thirdly, this is essentially motion sickness and if you feel it coming on, pause, look at something stationary next to you, then out the window at something across your garden (ie, at a distance). This reassures your brain that you are in fact still. Also taking a walk down the hallway and back adds to reassure your brain that its perceiving motion right.
Fourthly, this is heightened by anxiety/frustration and happens when you're struggling the most in a game and become tense and very focused. Sit back and remind yourself that it's just a game and it's fine even if you lose. Take some deep breaths
through your nose and focus on them, think of how the
cool air is coming in through your nose, cooling you, and breathe out
through your mouth and focus on how the
warm air is coming out, leaving you cool.
How motion sickness works is that your brain thinks you're poisoned because you senses are behaving erratic, in this case because some say you're moving and others not, so it attempts to eject the poison from the most likely place you're likely to have been poisoned, eating, by making you feel queasy and vomit it out. You being tense/anxious adds to your brain believing you're in distress and poisoned. If your brain is reassured that you're not poisoned, the symptoms will recede.
Taking these steps (that I figured out, not read) has helped me and should help you. The basic idea is to play calm and relaxed, with the screen only taking some of your field of view and the symptoms should not come, or be very mild.
EDIT: Oh yeah, and I forgot; whenever there's a loading screen or something, try not to look at the screen, but at some items across the room or at a distance, so that your eyes can adjust their focus a little. It delays the onset of the symptoms. In fact, make it a habit to use the loading breaks, etc, to do the above steps and you should not suffer from this again.
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<<<me
