It is natural to get tired, it happens to me too, I call it burnt out, after like an hour or two you just get tired/bored, it is a combination of music, drunk people, screaming your lungs out because the music is so loud etc.
I like a post made by Sinn which you probably can relate to:
http://sinnsofattraction.blogspot.com/2 ... eople.html
It talks about that if women did not go to clubs or bars 99% of guys wouldn't go to the clubs/bars, why because only like 1% goes to the club specifically to dance and enjoy the club SPAM....