Is it normal for my personallity to switch like this?

sometimes when i socialise i am the life of the party, funny, quick, always have something to say good at meeting new people, striking up conversation, good with the ladies etc, but then on the flip side i get times when im just silent, cant find anything to say, my heads not thinking much, it feels like i dont know or want to know my friends, and i get awkward like if someone talks to me i cant look at them in the eye or find much to talk about, its starting to get me down because i dont feel like me when this happens. i would say for every 3 good times i get 1 bad, and people do notice. im not depressed or anything, also when i do get a bad turn, if im out drinking i cant get drunk, is there some kind of switch in your brain? or am i mental? do other people get anything like this??