Pending transaction disappeared... what do you make of it?

i had a transaction pending for a purchase i made a hospital pharmacy (kaiser) my checking statement said that they were going to take $30 from my account for the pills. today i check the statement and it says that they didn't charge me at the transaction disappeared all together. i'm a broke *** student and would love the extra money, but don't want to risk an over draft in case it comes back all of a sudden. so i guess my question is, should i expect to see it come back or should i just enjoy the extra $30?