You wake up one morning and you look like you've been put together by Dr. Frankenstein: a wide-open eye, lopsided smile, droopy face, inability to raise an eyebrow, or maybe total paralysis on one side of your face.

After the initial shock and before you panic, go to the doctor, says Said Beydoun, M.D., professor of neurology and director of the electromyography laboratory at the Keck Hospital of USC.

Chances are you will learn that you have a frightening-looking-but temporary-condition known as Bell's palsy.

A benign weakness of a portion of the facial nerve, Bell's palsy is not life-threatening and tends to improve within a matter of weeks, explains Beydoun. It is caused by an inflammation of the part of the facial nerve that passes through the skull just behind the ear. "If we see the patient in the first five or seven days, we can use steroids to hopefully reduce the swelling," says Beydoun.

Physicians do not yet know what causes Bell's palsy, although scientists are researching a possible link to the herpes virus. It tends to strike younger men and women between 20 and 35 years old, pregnant women and diabetics. Although Bell's palsy may appear suddenly overnight, the usual course is to develop increased one-sided facial drooping over a period of a few days.

The important thing, Beydoun emphasizes, is to be evaluated by a physician to rule out other conditions that can mimic Bell's palsy: tumors, trauma, ear infections, Lyme disease or stroke.

"Most Bell's palsy patients are fully recovered within three to four months," says Beydoun. "But when you first look in the mirror, it can be one of the most frightening experiences you've ever had."