(One of my uncles told me this one recently.)
[Ed: Submitter sent this in rot13, but it doesnt meet my criteria]

A middle aged businessman goes to see his physician.

Doctor, Ive got this problem, the man says. My secretary, she
loves to give blow jobs. Every morning when I get to work I get a
blow job. She gives me a quick one before I leave for lunch.
And before I leave work at the end of the day she really works
me over.

So what seems to be the problem? the doctor asked.

Well, you see, my wife is a nymphomaniac, the man continued.
I service her every morning when we get up. I go home for
a quick half hour every day at lunch and then we have a
marathon session each night before we go to sleep.

I still dont know what your problem is, said the doctor.

You see Doc, every time I masturbate I get these dizzy spells.