I also thought I bombed the interview I had when I got my current job. Honestly, it probably wasn't as bad as you think. I don't want to downplay it, because it really sucks if you don't get the job, but interviewers do understand a certain degree of nervousness, and if the questions were complicated they know that too. I agree with BlackStilettos - send a thank you note, that will give you an opportunity to express yourself coherently and build yourself back up.