Sciatica

A pain that radiates up and down the sciatic nerve (primary nerve of the leg.) Spinal injuries are the most common reason for sciatica, though it may also be caused by tumors, abscesses, blood clots, or simply by incorrect posture. Treatment consists of bed rest and analgesics; they symptoms usually disappear within a few days.
Sciatica, being one of those conditions little understood by the general public, is an excellent excuse to stay home from work. "My sciatica's acting up again" is a colorful and quaint complaint, and since the average Joseph has no idea whether or not it's contagious, he's likely to grant you a respite from work until you are better. (Rabies is also a splendid excuse to stay home from work, but generally only works once.)