I know it's scary, but after having had two endoscopies myself, along with a manometry I can honestly say it's not nearly as bad as you're making it out to be in your head!
The kind of drug they use during an endoscopy is versed. It doesn't actually knock you out like general anesthesia does, but there are still some risks. Versed basically erases your memory, so in effect you are fully conscious, you just won't remember it.
And you won't remember much for a while after, so be absolutely sure you've got someone with you who can help you get back home safely! Don't even consider driving yourself, and you may want to plan to take the entire day off work.
When you get there, you'll be set up in a bed with an IV in your hand. This will allow them to provide saline and the versed for the procedure. You'll have a nurse take your medical history, and when it's time they will wheel you into the room. You'll be asked to lie on your side, and they will place a bite block in your mouth with a strap around your head. It looks something like this:
i01.i.aliimg.com/photo/v0/1492879435/Plastic_Disposable_Endoscopy_Bite_Block_of_Mouth.jpgThe bite block will help keep your mouth
open and guide the endoscope tube during the procedure. This is probably about
the last thing you will remember. The nurse will notify you that they are administering the versed, and your next memories will likely be someone telling you it's over, and walking to your car.
If you're anything like me, you'll spend the next couple of hours telling whoever is with you, "Hey, so I think I'm starting to remember things again!" only to have them tell you that you already said that 20 minutes ago. If I ever have to have another one, I'm going to go home and see how many times I can watch Groundhog Day before my memory comes back all the way :p
The only side effects from the procedure in my case was a dry/sore throat for the rest of the afternoon, and intermittent drowsiness.