Legendary folk singer Joni Mitchell's health scare is drawing attention to the fact that she's said in the past that she has Morgellons disease, a rare and controversial illness characterized by a crawling sensation on the skin with no apparent cause.

Mitchell was found unconscious in her home Tuesday and rushed to the hospital, according to her official website. As of Tuesday night, she was "awake and in good spirits," the website reported.

Health experts say there could be any number of reasons Mitchell, 71, collapsed, but Morgellons disease probably isn't one of them.

Morgellons disease is a mysterious condition, prompting experts to debate whether it is a skin condition, a psychological condition, a neurological condition, an allergy or something else, said Dr. Kevin Cooper, who chairs the dermatology department at U.H. Case Medical Center in Cleveland, Ohio.

These patients feel that there's something wrong with their skin, causing them to scratch and dig at it, creating open wounds and scabs, he said, adding that they don't always believe they caused the wounds. They often bring bags to dermatologists containing "fibers" they pulled from their skin, but these fibers can be anything from their own hairs to cotton fibers that had become stuck in their scabs.

"Generally when we biopsy it, we don't see much," he said. "Just erosion. The top of the skin has been scratched off or died spontaneously. So patients are pretty miserable."

Many Morgellons patients think bugs are crawling on their skin he said, but when they exterminate their homes, they find nothing, Cooper said. Some are diagnosed with delusions of parasitosis, but they don't agree with it, he said.

Cooper said even when nothing's touching you, there's a sort of "static hum" of sensation that your skin feels. For patients with Morgellons, Cooper said perhaps that hum is turned up, resulting in a crawling sensation.

Other symptoms include fatigue, short-term memory loss and trouble concentrating, according to the Mayo Clinic website. Middle-aged white women are most likely to have it, according to the site.

He said the disease is vague, varies from patient to patient and could have multiple causes.

The Centers for Disease Control and Prevention studied a cluster of 115 women in northern California who said they had Morgellons disease. Investigators concluded in 2012 that the illness was not caused by anything infectious or environmental.