Hiya Isabella,
Sorry for the late response!
First I would like to say that I am sure you will be just fine for the endoscopy, I have not has one done myself but my step-dad has and he said it wasn't so bad at all. I am sure you will do just great. As for GERD whatever that means, if it has to do with acid reflux, Nexium will be great to help it. I am often dealing with really bad acid reflux problems to the point where my chest hurts from it and as such have been put on Nexium before. Just got a new precription of it recently lol. It really helps. For me the pain left really quickly and the acid reflux was gone and I don't remember having side effects of it at all. I am stareting my new prescription in the days to come lol. Btw, If you want more information on side effects I find that the best people for that are pharmacists. Most of them have computerized systems that enable them to print out a sheet on a specific medication which has the side effects listed on them. and they can even discuss the pros and cons of that medication with you. I find that for medication information pharmacist are great and underutilised lol. anyway, hope this helps a bit!
-diva