I've been using ASUS MG279Q monitors for about 3-4 years now (27", 1440p, 144hz, IPS, flat), and a single ASUS PQ321Q before that (32", 4k, 60hz, IGZO, flat). I never got sick with those.
I recently purchased 3 Samsung Odyssey G7 monitors (32", 1440p, 240hz, VA, curved) and within 30 minutes of using them, I start feeling sick. It's like a nauseating, lightheaded feeling in my head, not in my stomach or anywhere else. I tried 240hz, 144hz, and 60hz, no effect. I made sure to bring down the brightness level to something sane like level 17, and I even tried blue light filter mode. None of them affected how I was feeling. To make sure it wasnt a fluke, I put back the ASUS monitors and I started feeling better after a day. I used the ASUS panels for 2 more weeks, no issue. I then put back 1 of the samsung curved monitors (just a single one this time). Whenever I did any work on the curved monitor (requiring me to look at it), I started feeling sick again. If I moved my work to the flat panels, I started feeling better.