We had one at work just yesterday. We were all standing round in the office eating cake, most people drinking champagne etc. I was okay, no meltdowns but I felt pretty horrible. Some people made conversation with me (mainly small talk) but I eventually went to the toilet then walked around the city for a while, then just got back to work.
It wasn't enjoyable at all for me and afterwards I felt really tired. I've never been invited to a party like the ones I hear about at school (huge amounts of alcohol, insecure teenage girls kissing anything that has lips, male or female, and then bragging about it at school the next day), thank goodness! It's not my scene at all.
Like a lot of people have said, I can't hear what people are saying over all the other noise so they have to repeat stuff for me. I end up having awkward moments and feeling stupid pretty quick.