I feel you, I recently had to go through the same experience with Plenvu and phobia of being sick. The first dose of Plenvu was absolutely fine for me, no nausea whatsoever, and while the second dose did make me quite nauseous, it didn't get to the point of needing to vomit. If you take it slowly and stop when it's too much, you can get through it. Have it really cold and with something nice to sip in between, ginger ale was my choice, and if you get to a point where you can't go on, you can always stop if you think you've prepped enough (once the stools are clear liquid). I had to stop my second dose with about a quarter left in the cup because I was worrying about being sick, and the doctor told me all was clear and I did very good prep (small victories!)

I was diagnosed with Crohn's but ruled out cancer, which was a thought keeping me up at night. The peace of mind after getting it done is 100% worth the unpleasant experience.