They don't usually give general anaesthesia for endoscopies, they use twilight sedation, often times Versed. Versed is a benzodiazapine which makes you sleepy, extremely relaxed and you won't remember or feel anything. It also has some anti emetic properties, so it shouldn't make you feel bad, but you can always ask for an additional anti emetic just to ease your mind a bit. You'll be ok.