One of the best-known sleep disorders is narcolepsy, a serious medical condition that causes sufferers to be suddenly overwhelmed by feelings of fatigue. But narcolepsy symptoms also include abnormal episodes of "dreaming sleep," which are similar to hallucinations, and attacks of "cataplexy," in which a person loses control of certain muscles for a few seconds at a time.

One in every 2,000 Americans has narcolepsy. Here are a two you may have heard of.

Believe it or not, Harriet Tubman was a narcoleptic. The African-American abolitionist who freed hundreds of slaves in pre-Civil War America is famous for her strength of will, but less known for her weakness for sleep. As a 12-year-old girl in Maryland, Tubman received a serious blow to the head from her slave master. She never fully recovered, and the injury was said to cause her intermittent bouts of narcolepsy from which she suffered for the rest of her life.

President Clinton's former deputy chief of staff, Harold Ickes, was a long-time friend of Clinton, but around the White House, he was known as a strange bird. During staff meetings, he stood in the corner and took notes, rather than sitting around the table. But Ickes wasn't being rude; he was trying to keep from falling asleep. Ickes started experiencing symptoms of narcolepsy at age 25 when he entered Columbia University Law School. To help keep himself awake, he took obscene amounts of Dexedrine—about 60 milligrams a day, a normal dosage being around 5 milligrams.

But if Ickes was bitter about his sleep disorder, he certainly couldn't blame it on his genes. Ickes' father, Harold LeClair Ickes, was also an advisor to a president, Franklin D. Roosevelt, and a member of his cabinet. But unlike the younger Ickes, Harold LeClair was a life-long insomniac, never known to get more than three or four hours at a time.

More on sleep: Sleeping On The Job, Five Disorders That Make For Scary Sleeping, Should You Wake A Sleepwalker?

["The Sandman Cometh" was originally printed in mental_floss magazine, Volume 3, Issue 1.]