Macbook Pro battery capacity drained overnight - help!

I've had my Macbook Pro for about two years now, and have never had any battery issues. Today, out of nowhere, the capacity went from about 91% to 20%. What on earth is going on? Calibrating the battery didn't accomplish anything.

i guess the best thing to do is to go to an apple store. which mac do you have, so we can further advise you?
my friend had this problem and the store replaced his battery for him... good luck!

You may be a candidate for an SMC reset Link - if not and it shows no sign of charging - perhaps a trip to the Apple store is in your near future.