db, you honestly don't know why you didn't get the job.
maybe it had to do with the interview, maybe not.
i agree that often, it has to do with how you clicked w/the interviewer.
as suggested, i would send them a note, thanking them for their time/consideration, and that you'd truly appreciate any feedback as to how you might improve your interviewing skills.
it also wouldn't hurt to let them know how nervous you were, and that you fear your anxiety may have disqualified you from being hired.
sometimes when you show the human side of you, it makes you more desirable as a candidate.
i remember one interview i had many yrs ago, where i kept on tripping over my words, followed by nervous laughter and persistent hand-to-neck gestures, which is what i do when i'm nervous.
i CLEARLY messed up and was hired anyway, because the interviewer found me "simply charming and adorable" as i struggled through our time together.
so in essence, i was hired because i was so darned pathetic.
but because i didn't have an ounce of pride, i took the job.
you just never know why one may be hired, or not hired.
but you have nothing to lose, by asking for input.
wishing you the very best.