One time I boarded a 12 hour long international flight. The plane taxied out to the runway just as a dense fog was descending. It was deemed too dangerous to take off and too dangerous to even taxi back to the gate. It took all night for the fog to clear (over ten hours) so I definitely fell asleep and woke up again while we were still on the tarmac. Then we had to wait for them to restock all the drinks and food that had been consumed overnight before we could finally take off.