I wake up at 5:30 when my alarm goes off. I allow myself to just lie there a few minutes.
When I next wake up, it's 6:50, which means I'll be late for work.
But when I go into the living room, I see a clock that shows it's 4:40, which means I woke up early and only imagined it was time to get up (which has happened before). Different clocks show either the 6:50 or 4:40 time.
I realize the two clocks that show 4:40 are both quartz -- I actually see the motion of the second hand on one of them as it ticks off each second. Since these would be the more accurate clocks, I go back to bed.
Then I wake up. That whole bit of looking at different clocks had been a dream when I dozed off for a few minutes after waking up at 5:30. The dream is over. Or is it?