That's great that your mum will be with you, before and after, for your upper endoscopy.
My personal tip is that for every medical test, appointment, or surgery, it is tremendously helpful to schedule something right afterwards (that you will be able to handle in your condition), that you consider to be a treat. For my husband and I, our standard option is that the "victim" for the occasion gets to pick the restaurant of their choice afterward. For many procedures, you aren't allowed to eat for hours (or sometimes even days) beforehand, so the restaurant date also provides much needed nourishment in a hurry. And for that reason, we usually know of a few good restaurants right by the clinic.
It doesn't necessarily matter that it's a restaurant. Maybe for you it will be going to a movie. Whatever it is, though, be sure to set your heart upon it ahead of time and to put your mind on looking forward to it. Then whenever you are tempted to worry about the appointment, in any way at all, take that as an opportunity to switch your thoughts over to the GREAT time you are going to have afterwards (at the restaurant, movie, coffee shop, or whatever you have planned.)
This helps keep fear from running away with you and keeps you focused on something fun and positive, which the person accompanying you will really appreciate. My husband and I also make a point of always bringing a good book with us to all appointments. Then if -- or should I just say WHEN -- your appointment is running late, you can just happily exclaim, oh great, I get to read another chapter!
It takes a force of will to move your mind to the positive aspects of the appointment. But if you force yourself to see the amazing scenery on the way to the clinic, the wonderful or at least interesting people you meet at the clinic, the great time you had reading your book, and the fabulous meal or treat you are going to have afterwards, then you will find your mom, and even others, eager to go along on any other upcoming appointments. And you won't be boring your friends with details of the ucky procedure but rather with all the great fun you had, surely adding more sparkle to a sunny personality and not letting the time-consuming chores of illness drag you down.
Please let us know what you plan, and how it all turns out, okay?