Both my daughters are on waiting lists to have this done,my eldest is 20 and has been waiting almost 5 years as our local hospital has no orthodontic surgeon at the moment. My 18 year old is pregnant so can't have hers done yet either even if there was a surgeon. I have seen the operation on a cosmetic surgery programme and it looked horrific,the poor girl's face afterwards was unrecognisable.The doctor will ensure you are given adequate pain relief after the op so I wouldn't worry about that too much.
I wish you luck with your procedure and hope it all goes ok for you.x