GP giving you diazepam is different, that's a prescription, you walk away with controlled medication unsupervised. Some are unsympathetic and some just don't want to take risk that something will happen and they'll be responsible as they prescribed.
However it's completely different in a hospital environment, they give you a medication direction, so they are controlling how much you can take, when they give you it, then they supervise you for a few hours after and make sure someone collects you. Plus they'll be able to see you are uncomfortable by pulse rate, things like that, so know you aren't drug seeking (plus it would be a bizarre way to drug seek!). So they are fine. It's also routine for them to do this. They gave me temazepam, extra strong from the diazepam group even though has no tolerance, because I walked into the room, cried then couldn't stay. They decide what is appropriate for medication and dosage for each person. When I hadn't felt comfortable enough, they gave me another dose. I was then able to sit still for the brief seconds needed
Tell them when you arrive, they'll take care of you.
Plus, do it! I can't believe what a fuss I made over nothing, it was phobia reaction. Doing it makes you lose a bit of the phobia and be more comfortable in future, it's a type of therapy called exposure therapy.
As I said, I have since gone through so many surgeries I actually can't count, IVF which is needles, blood tests and more every single day for ages, now I'm comfortable. I broke my knee and needed a surgery, I was joking with the consultant and he was playing a Stevie Wonder song on his phone after we'd joked about it in a consultation. I was literally dancing and laughing with him as they did the anesthetic. The nurses said later that they thought I was reacting to sedation meds, they were laughing and surprised to hear that no, I was actually just laughing and messing around, in an operating theatre, with a surgeon.
When you have something serious, that's terrifying, trust me. When it's not serious, be relieved about how relatively easy it is (broken knee is not going to kill me, so I was lucky and therefore happy and fine) and go for it.
Benefit is you shake off the phobia.
I got every vaccination in the world (including helping the nurse do my own whilst we did several at once) and botox after all the insane amount of stuff I went through! I no longer cared at all about needles, so figured may as well get some tiny positive thing from difficulty lol:)