This guy wakes up out of a deep sleep and, feeling real horny, nudges his wife awake and asks, "Why don't we get it on, eh?" 
She replies, "I have an appointment at the gynecologist tomorrow and you know I don't like to make love the night before." 

So the husband agrees and rolled back over and started to go back to sleep. 
A few minutes later, he nudges his wife again and asks, "You don't by any chance have a dentist's appointment tomorrow, do you?"