Everyone's pain level is different.
Before I got professionally waxed, I also watched YouTube videos (and "40 year old virgin")...seems to me many of them were excessive in their reactions.
Just in case, though, I got a DIY waxing kit and did my legs...the pain, for me, was totally bearable (no pun intended). At the salon, I handled the entire upper body (front and back, and arms) without so much as a whimper. The tech tells me that some do, some don't handle the pain.
Don't drink any caffeine products before going in...take 1-2 Ibuprofen an hour before going (it numbs the pain receptors), trim hairs to about 1/2" (12mm) as long hair will need to be trimmed anyway.