I've experienced this is different ways. I think, in general, our bodies and minds are used to sleeping about 8 hours. So on most mornings, the familiar feeling when you wake up is "yeah, I got an average night's sleep of about 8 hours." It feels normal. And it's somewhat common to get an hour more or less than average and you can recognize what that feels like too. But when you have an very unusual amount of sleep, like a nap, the feeling is unfamiliar and the clouded mind is likely to misjudge the passage of time, either too much or too little. It's only because it's unusual and your mind makes a hurried guess. Other factors like illness, medication, or sleep deprivation can contribute to the unusualness of a sleep period.

If your sleep situation is unusual, you mind tends to be more alert and cautious. And this can lead to improved chances of lucidity. For example, I have great success becoming lucid when I've slept in a hotel. Other techniques along these lines are to sleep in the opposite direction of your bed (foot to head instead of head to foot), or to move from the bed to the couch.