I think my drink may have been spiked?

I was out on New Year's Eve...I had had a few drinks..no more than I've had before and I was having a good time with all my friends. My girlfriend said I left for about 20-30 minutes and came back a different person like she's never seen me before. She said I was aggressive and that I left the night club. Outside she said I was aggressive and verbally anusive towards her and then I began crying also and calling myself a loser, telling her to leave me alone. She said I was not slurring my words or falling over or anything. And the next morning I could not remember a thing? Does anyone have any ideas what could've been the cause of this? I'm not an aggressive person by nature and nothing like this has ever happened before? I'm with my girlfriend two years and nothin like this had ever happened. Friends of mine also said I wasn't myself that night and even the next Mornin they said my hangover wasn't what it should be! Any help please? Thanks