I feel your pain, I had the same when I switched from my old monitor to the new Dell Alienware AW2521HF. I had such symptoms that I thought I was dying, really. After many days of trying, I finally managed to set it up so that it is more or less OK, but I still feel uncomfortable with some games. I think the new display technology will be a dead end for many. All that remains is to adopt or abandon the new technology. There is also hope that someone will eventually figure out what the problem is, but I would rather not count on it.
And some practical advice from me:
1. Change monitor manufacturer, DELL unfortunately often causes problems.
2. Try different settings with your monitor. What worked for me was setting the contrast/brightness to 38%, setting the white balance to warm and setting the refresh rate of the monitor to static 240Hz (I turned off G-Sync). Interestingly, when I change the brightness to, for example, 40%, after a few seconds I want to vomit.
3. Eye training. It may sound strange, but regular eye exercises can help (circular movements of the eyeballs, eye accommodation exercises, etc.).
Good luck and don't give up.