Bombed the GMAT.Thanks to a hangover. Angry at myself

I don't even know what to write in the debrief. I was hoping that I'd do well but here I am sitting disappointed. Took the GMAT and got a meagre 640.

I had studied quite well for the GMAT and preparation was not the reason for my poor performance. I had studied in a fairly systematic way and had finished OG11 and 12. Had also done Aristotle SC Grail ,Manhattan SC Guide,CR Bible and Aristotle RC Practice sets. The hardwork was evident in the fact that I was averaging around 700 on the practice tests. Though I did not get 730+ scores on the practice tests, but surely I was doing fine given that I hadn't set a crazy target and was aiming at 720 which would have been good enough for me .

Everything was fine till the day before the actual test date, I had some college friends coming over to Delhi and we were meeting after a long time. I did not want to study the last day and wanted to unwind and thought that this will be a good opportunity to relax and get the anxiety off me. We met in the evening and I had a few shots in a pub. Usually I have a huge capacity to gulp down and thought that a few shots wouldn't do harm,rather it'll help me sleep well. Everything was good; came back from the pub at 12 which is fairly a reasonable time.But I somehow started feeling giddy after that and I just could not sleep. My head was aching and realizing the fact that I have to sleep on time, I could not even fall asleep. It must be at 3-4 am that I feel asleep .
I had a morning slot and somehow I managed to get up on time but the hangover was still there.
I knew that I would have a hard time concentrating during the exam and that's what happened on the test. Phew!

I'm not sad but just angry with myself for being such a jerk.How can I be this stupid to "assume" things. I'm really mad at myself.Don't even feel writing more. Have posted this on another forum also but posting it again so that you become beware of doing such stuff like I did.