A son calls his elderly father who's in hospital after a hip replacement and asks him how he is.
'I'm fine,' says the old man. 'They're really looking after me here.'
'Are you sleeping OK?' the son asks.
'Oh yes. I get a solid ten hours. Every night they bring me my hot cocoa and Viagra tablet and I go out like a light.'
The son is horrified and calls the hospital back and demands to speak to the ward sister. 'What the hell are you doing giving my old man Viagra?' he shouts. 'Are you trying to kill him?'
'On the contrary,' says the sister, 'it works very well. The cocoa knocks him out and the Viagra stops him rolling out of bed.'