Fred wasn't feeling well so he went to the doctor who performed a complete checkup, numerous samples for the lab etc.
The results were bad, "Fred, you've only got 24 hours to live."
Fred rushed home to his wife and told her the news.
She suggested they immediately go to bed for some loving.
A bit later Fred says, "Dear I can go again and the clock is ticking."
They knock one out and fall asleep.
Fred wakes up, looks at his watch and nudges his wife awake,
"Dear there's only 19 hours left." They do the deed and fall asleep again.
Fred wakes one more time several hours later, looks at his watch and gives her an elbow in the ribs, "Come on love, one more!"
She opens one eye and says,
"Fred, I'm exhausted and I have to get up in the morning. You don't!"