What are the reasons for your endoscopy?
With the exception of my very first endoscopy, I've had nothing but good experiences. My first one had to be abandoned because I had a narrow stricture - so narrow they didn't have a probe that would fit. I ended up waking up under sedation and coughing, and the probe ended up damaging my esophagus somewhat. But please be aware, my stricture was much worse than they anticipated and that's why it went down like that.
My next "scope", and all of the subsequent scopes, have gone wonderfully in terms of procedure and recovery. Where I go, a 12 hour fast is required. When I arrive they send me to a prep room where an IV is put in my arm and I am delivered fluids and a relaxant for about 30 minutes. They take me into the procedure room, go over things once to make sure I know what their plan of action is, and then they sedate me. They use a bit more, since I woke up the first time. Let me tell you, it's the best 20 minute nap you'll ever have.
In the procedure room itself, I am given oxygen via one of those breathing devices that slides under your nose. Also, just before I doze off, they place a plastic ring in my mouth to hold my mouth open. They then send down their probe, which is equipped with a camera, and check things out. If my stricture requires it, they also send a small, narrow balloon down and expand it to dilate my esophagus. Finally, they take tissue samples from various places for biopsy. The biopsy checks for a variety of conditions (not just cancer or barrett's).
They start to wake me up as soon as the instrumentation is out of my mouth, and it usually takes about fifteen minutes for me to come around completely. My wife (who is always my companion on these trips) is briefed by my doctor as soon as the procedure is done and then joins me in the recovery room. She relays whatever instructions the doctor has (he usually doesn't come back in himself).
Overall it's a fairly brief and very painless procedure. Nothing about the process makes me nervous anymore. I've had it done six times now and my seventh is next week, so it's fairly old hat to me. The only times I get nervous about it are when I'm waiting for the biopsy results to come back. My first successful scope resulted in me being diagnosed with barrett's esophagus; at the time it was low level with no disphagia. That was 16 months ago. I'm hoping my scope next week shows something similar or better, but my reflux symptoms have come back in the past 2 weeks so I dunno.
But yeah, overall it's a pretty easy procedure to have to go through. There's very little to be concerned about in terms of problems arising from the procedure itself. That thing that happened to me the first time was kind of a fluke, and one specific to my esophageal problems at the time.
After the scope and after any test results come back, your doc will formulate a plan for you, which could range from doing nothing at all to changing meds to scheduling further scopes. It depends on why you're having one done and what he or she finds once they get a look inside.
My best advice: don't stress. It's a simple procedure with very little risk, especially if all they're doing is taking a look around and getting samples for a biopsy.