So I realised something while being nauseous on reserve today. I've never had this problem with much more violent headbob, like when you're sprinting, crouchwalking or limping. Probably has something to do with my brain realising that it can't be real and to not worry about it (boring explanation of why you get nauseous at the end).
So, while it seems counterintuitive, I turned the headbob up. At 0.5 it got better, but I was still a little nauseous. At 1.0 I was rocking out to Black Sabbath but I wasn't nauseous. Quick note – it didn't seem to affect my aim – my laser doesn't move any more than normal, just my viewpoint.
Boring explanation: The nausea is a form of motion sickness. Essentially, your brain sees the cues to movement, but also realises that you're not actually moving. So, it figures you have ingested a toxin and tells you to get it out. It's the same problem many people have with VR. By making the movements so dramatic that they can't possibly be real – no nausea.
Worked for me, hope it works for you.
Source: https://www.reddit.com/r/EscapefromTarkov/comments/fiqyyx/headbob_nausea_fix/
