An extremely modest man was in the hospital for a series of tests, the last of which had left his bodily systems extremely upset. Upon making several false alarm trips to the bathroom, he figured that the latest episode was just that, so he stayed put.
Suddenly, however, he filled his bed with diarrhea and was embarrassed beyond his ability to remain rational.
In a complete loss of composure, he jumped out of bed, gathered up the bed sheets, and threw them out the hospital window.
A drunk was walking by the hospital when the sheets landed on him. The drunk started yelling, cursing, and swinging his arms violently, in an attempt to free himself of the sheets. He ended up with the soiled sheets in a tangled pile at his feet.
As the drunk stood there, staring down at the sheets, a hospital security guard who had witnessed the entire incident, walked up to him and asked, what the hell is going on?
The drunk, still staring down at the sheets, replied, I think I just beat the **** out of a ghost.
i didnt get it
i just understand medical terminologies 
yeah i got this joke till here