What could have caused my GFCI to trip, and what can I do about it?
I have seen surges or dips in voltage trip GFIs. Can't explain why, but I have seen it.
Also, older GFIs were slightly more prone to nuisance tripping. If they are more than a few years old replacing them would not hurt one bit.

These two are not on the same circuit by any chance are they? I sincerely hope not, but it would explain things.