A chap goes to the doctor's because he's been sunbathing to long and has got terribly burnt.
"yes" says the doctor, after examining the chap's whole body "its definately sever sunburn. I'll write you a prescription."
Checking to see what the doctor has prescribed, the chap was surprised that he had written down calamine lotion and viagra.
"that's odd", said the chap. "I can see the need for the calamine lotion, but why the viagra ?"
The doctor replies :
"That's to keep the sheets off you at night".