"What the heck was I thinking?'
"What the heck are you thinking?"
"What the heck is up with this weather?"
Sometimes 'heck' gets substituted with 'hell'. Same meaning, just a little stronger statement. (I bet most people in the eastern United States are saying it a lot).
I utter this statement after a night of too much partying and I'm paying for it with a queasy stomach and headache. Plop, plop, fizz, fizz, oh what a relief it is.