Your brain is incredibly powerful, so something being “all in your head” is pretty much the whole ballgame.
I can’t speak to pre-chemo nausea, but used to get nausea whenever I traveled—mostly it was a mix of adrenaline and exhaustion, but like you, it was “just” in my head. I found that mindfulness meditation helped a great deal, especially the breathing excercises—my teacher related everything to biological processes, which helped me a lot (my favorite bit from her was ‘the brain is digital, the body is chemical’—so an instant reaction in the brain triggers a longer-lasting response in the body). I found just concentrating on breathing helped a lot, as did identifying my triggers. There are apps that can guide you through the steps (I use the ‘calm’ app) and lots of online resources you can find with google.
Also, and this is going to sound weird, I just accepted that this was how I rolled. I got pretty zen about getting nauseous, accepted that it was how I reacted to stress and made accommodations. Of course, once I’d done that I stopped feeling nauseous, because brains are powerful things that like to keep us guessing.
38 yr old female
Rectal bleeding for 1 month—>
5/4/18 colonoscopy found mass in sigmoid colon
stage 2a, 0/17 lymph, clean margins
LVI neg, PNI neg, MSS
9/21/18 CEA 0.8
11/16/18 CEA 0.8 & CT clear
12/7/18 iron infusion
2/1/18 iron improved, CEA stable.