Over twelve hours? That's half a day.That is a while...hopefully it's just that once you fall asleep that you're a bit of a heavy sleeper. xP
Yes, it's very annoying because it feels like my day is completely wasted. I've started to tell people to wake me up at a certain time and to not let me go back to sleep. It helps, but I still find myself going back to bed.
It's also annoying because I can be tired for an entire day, but as soon as it hits 10pm, I am suddenly wide awake.