Hey,
I read all the horror stories online, too, and went in sweating buckets, but I'm here to be one of the positive experiences!
I had my IUS put in a week ago. I took 2 ibuprofen and 2 paracetamol an hour before the appt (more than recommended but I was scared lol). I'm sexually active but only 20 so never had kids, so was a bit nervous.
Anyway, the actual insertion was pretty painful, but nothing like the stories I'd read. I can only describe it as a very bad period cramp lasting about a minute; the pain isn't localised, it just feels like a cramp. Once she took everything out the harsh pain stopped and I was left with normal period cramps.
For the rest of the day I had mild cramps, just like a period, and the tiniest bit of spotting, but since I haven't had anything! No cramps, no bleeding, I don't even realise it's there.
I hope this gives you some consolation that it can be fine! I would definitely take the 1 minute of pain for 5 years of contraception!