Little-understood 'Restless Legs' can make sleep an elusive dream.(The Dallas Morning News)

A strange medical condition has been robbing Bob Whitehead of sleep since the mid-1980s.

"It feels like worms or snakes are crawling up the inside of my legs all night long," says the 57-year-old former public official.

The symptoms got so bad that Whitehead took early retirement last December as director of public works in Colleyville, Texas. He was worried that his lack of sleep was compromising his ability to oversee the dramatic growth of the community just outside Fort Worth.

"I had a general feeling of not being able to do my job mentally because I was so sleep-deprived," recalls Whitehead. "Retirement has allowed me to take a nap in the afternoon."

Whitehead's mysterious condition is shared by an estimated 12 million Americans, many of whom are forced to modify their lives because their legs won't let them sleep through the night. Although certain medications have been shown to reduce the symptoms, the syndrome ranks as the fourth-leading cause of insomnia. Stress, depression and anxiety are the top causes underlying sleep disorders, according to the National Sleep Foundation.

Still, researchers around the world have been unable to unlock the mysteries of this restlessness, other than to agree that it is a neurological disorder. They also have concluded that it strikes more women than men. Children get it. So do some women during pregnancy.

But nobody can say why.