I had the same thoughts "but won't i feel it THEN?" when I was getting an upper endoscopy. The anesthesiologist said you're in such a trance, dreamlike state plus with the inability to form memories its like you're not your real "consciousness" but something different. Sort of like your brain is in "limp mode" and its not really _you._ This was both comforting and slightly terrifying in a different way.
I've had an upper endoscopy and a colonoscopy, both the same day, and both without anesthesia. If they didn't take a biopsy, it likely shouldn't have been too traumatic, consciously or subconsciously - maybe that's a bit comforting to know.
I do remember my lung biopsy where they went in down my neck. Maybe they give less drugs for that than for your upper endoscopy. My memories have a slightly horror movie vibe but I would not be put off having the procedure again.
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Obviously it would be worse if you remembered it, but the trauma is still there even if you don't. Ask Bill Cosby's victims.
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