Dear Veronica
firstly, let me assure you I would no be replying unless I had this procedure myself. I did, although some years ago, so what I have to say should be comforting, especially as I imagine things have improved since my experience.
I had the procedure for the same reason as you. they tried examining my throat without resorting to this procedure, but I have a very low threshold gag reflex and they couldn't do it any other way.
I was and am still on Diazepam too, so our circumstances are very closely aligned.
Let me tell you, I was terrified at the prospect of having this done to me, but all for nothing. I've had worse experiences at the Dentist. Honestly!
The staff and the specialist where caring, understanding, and re-assuring. I had almost half an hour to calm myself down before the procedure and the specialist came to speak with me personally to tell me that they never "force" this on anyone.
He said if at anytime I showed the slightest distress, they would stop immediately.
I won't go into detail, but this is what happened. I went into the exam room on a trolley. A nurse sat next to me and held my hand. They sprayed the back of my throat with anaesthetic so that I had no gag reflex at all, and when I told them I was ready they gave me an injection.
They asked me to count backward from ten. The next thing I remember is opening my eyes with a different nurse holding my hand, only to realise I was in another room and the procedure was complete. I couldn't believe it, as I had built up in my mind all kinds of horrible scenarios.
Rest assured, whatever it takes to relax you and allow you to have a distress-free experience, they will provide it.
I don't know when your appointment is, but whenever you have it, think of me thinking of you.
You will be fine. It's not like you imagine. x