question about canceling interviews

Hey folks,
I am supposed to have two interviews in a week or so, but I think I should cancel them, becuase I was accepted into a school I really like, and have enough other stuff going on that nnecessary traveling seems sort of silly. Unfortunately, it's such short notice! I have a good reason, because I just found out yesterday, but I feel really badly about canceling interviews only a week beforehand...though it's not like I did it on purpose, and it wouldn't make sense to go just to save the schedulers the hassle of having to try to find someone on short notice.

I'm planning to call the schools early tomorrow morning and let them know... is it okay to say I was admitted to another school, or should I just say something came up? I realize this is kind of silly, but I'm just trying not to step on anyone's toes. At first I thought I would re-schedule the interviews until January, when I'm less swamped, but I doubt the schools do that, and it's probably not necessary.

Also, does anyone else feel doubtful of their acceptance letters? Proof that I'm becoming neurotic is that I half-expect a little thin envelope to arrive next week "please excuse our mistake in sending you the wrong letter..." I hope that never happens to anyone!

sigh...mid-terms have hit my brain hard, so sorry if this sounds nuts.
back to studying,
elle