I've had 9 endoscopies at 3 different hospitals over the last 4 years, so here's my take on it - like you, I was also incredibly anxious before my first one.
Wear something comfy, like leggings, a t-shirt and a cosy hoodie and warm socks.
When you arrive, they'll take you into an office type room, where a Nurse will take your blood pressure, check what medications you are on/have taken that day, go through your medical history, why you have been referred for an endoscopy, what they are going to be looking for/are expecting to find, they will explain the procedure to you, ask if you would like sedation (I always say "Yes please, as much as possible!") and throat numbing spray (again; "Yes please!") and they will answer any questions you have.
You will then be taken to the 'ward', which is usually a bay of 6-8 trolley beds. Some patients will be there for the same procedure as you (they will be in their own clothes), others will be there for colonoscopies (they will be in gowns). You will wait on the bed here until your procedure and will be brought back to the bay afterwards.
If you have decided on sedation, they will insert a canula, ready for it to be delivered directly into your vein once you are in the 'Procedure Room' (PR).
When it's your turn, you will be wheeled on the bed into the PR, where you will be introduced to the staff. There will be either a Consultant or an Endoscopy Practitioner who will be performing the procedure, a Nurse who will be tending to you, keeping you informed of what's going on etc. and at least one other member of staff keeping an eye on your stats (such as heart rate, oxygen saturation etc.)
The Consultant will explain one last time what will be happening, they will check your name, DOB and hospital number and ask you if you have any questions.
The Consultant will then administer the numbing spray. You will need to open your mouth wide and stick out your tongue and they will pump a few sprays of a banana flavoured liquid into the back of your throat. You will be encouraged to swallow a couple of times and then will be asked to lay on your side on the bed.
They may put a disposable absorbent pad under your face, just in case you are a little bit sick/dribble a lot!
The Consultant will then administer the sedative through the canula. I have tried counting until it takes effect, I can never remember getting past 30 seconds.
The Nurse will ask you to open your mouth and bite down on a rigid plastic teeth guard and the next thing you know, you will be coming round in the recovery bay/ward bit, about 20-30 minutes later, with a mildly sore throat - ta da!
The Nurse will come round to check how you're feeling and do your obs (BP and oxygen sats), and once they are happy and you feel able to, you will be invited to take a seat in a waiting room, where packets of biscuits, cups of tea and NHS orange squash are to be consumed in abundance!
Once the Consultant has had a chance to review and pass on their findings from your procedure, you will be called into the office with the Nurse, who will explain the outcome and the next steps; ime, some or all of the following: a letter to my Consultant and/or GP, recommendations of new meds (to be discussed with Consultant), a requirement for a repeat endoscopy etc. and you will then be sent on your merry way!
NB: If you have sedation, you have to be collected from the department by someone as you are not safe to be alone for some hours directly afterwards and you are not legally able to drive for 24 hours following the sedation.
I dreaded the first one so badly, I didn't sleep for 3 nights in the run up to it, but it was honestly a complete breeze! Good luck OP, you'll be fine!