Antisocial For No Reason

Have you ever had a moment where you are surrounded by your friends and they are all having a good time and trying to include you, but all you want to do is sit in a corner and not talk to anyone? It happened to me just recently and I'm trying to figure out why I became so reclusive at this party for no reason. Especially since the party was to partially celebrate me and the end of the semester and all that I've been through. If anything, it actually made me feel more uneasy about myself (I was actually very happy beforehand, until they surprised me). I feel like such a brat but the entire time I just wanted to crawl back in bed...