kalashnikov

So I am currently a college senior (only a few more weeks to go!) I had a girlfriend the first year and half of sophomore year, and we had a great sex life (even past officially breaking up - though not into junior year at all.) Since then I have not had any long relationships. There were hook-ups now and then, and a couple short (a few weeks tops) relationships. None that had that great of sex.
The problem started a few hook-ups ago. About two months ago I was with one girl, and I couldn't get it up. A second time I did, but not easily, and the sex wasn't great. However, in retrospect I really was not attracted to her as much as just horny. I mean, she even chewed gum in bed. That just isn't hot.
A few weeks ago I met a girl at a party, and I was really attracted to her, and we went back to my place and I couldn't get it up (I blamed it on the alcohol, though that wasn't the case). She stayed the night and it worked in the morning.
About a week ago I invited a girl over to smoke, and one thing (obviously) led to another, and again, nothing the first time, and barely the second. However, unlike with any of the other girls, we talked about it a bit. I was starting to get pretty nervous: can you lose it all at age 22? masturbation has never been a problem.
I decided to see her again on Friday, had a drink or two before she came over and layed down with some music (because I was definately nervous), she got there, we got high, and proceeded to have fantastic sex about 6 times that night and the next morning (even with stopping to go to her place, which has a bigger bed)!!

So a) I am greatly relieved to see that not only does it all still work, but it can work great! (I have never so much sex in one night! Nor been so exhausted the next day!)
b) what's the deal? Is it about being relaxed? taking it easy? having the right level of attraction? being significantly over an ex? the right music (for the record, especially when high, Massive Attack is a fantastic band for sex)? self confidence (obviously failure and nervousness feeds back into itself)? a combination of all of this?
has anyone else experienced this?

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