Pre-engagement party

Last night it was the pre-engagement party of one of my friends whom I know for about 10 years now.
It was fun and everybody was happy, laughing and dancing, I was having quite a good time myself. A few flirts and dances aswell, so I guess I can't complain at all.
However this was a joyous occassion and nothing went wrong or against my idea's I found myself not being touched or dazzled or even slightly enthousiastic about anything that entire night.
I kept telling myself this is fun, this is a happy ocassion and I should be happy being here and I should be excited.
But the more I thought about it the less excited or happy I became. I guess I'm just unable to be truly happy. Eventhough I keep getting better at faking it.