I had an endoscopy-colonoscopy corabo three years ago. Other than the prep for the colonoscopy (all that stuff one has to take and running to the bathroom every fifteen minutes), I have no recollections of the procedure and had no side effects. I know I was awake talking to people afterward because my husband told me, and I don't remeraber anything until I came home.
I would tell the anesthesiologist (likely a nurse practicioner) about your previous experience so they use a type of anesthetic that causes retroactive amnesia. Then, you will not remeraber anything even if you wake up during the procedure. From what I understand the endoscopy is uncomfortable but not painful like surgery would be. Hopefully, you'll have a completely different experience. I think it is certainly worth the aggravation to be able to obtain peace of mind in return.
By the way, there is no prep for the upper endoscopy other than no eating or drinking from midnight the night before.
Rose