Joni Mitchell was hospitalized on Tuesday after being found unconscious in her apartment, according to the 71-year-old singer's website. In recent years, Mitchell has said that she suffers from many ailments, including a strange and controversial condition called Morgellons disease, The New York Times reported.

People who suffer from Morgellons say they have a bizarre range of symptomsincluding sensations of crawling or stinging on and under their skin, skin sores and the appearance of stringlike fibers that seem to sprout from the sores, according to the Mayo Clinic. Some people also report severe fatigue, problems concentrating and short-term memory loss.

Morgellons disease is not widely accepted as a medical diagnosis because there is no established physical cause of the condition. Some doctors say the mysterious fibers are actually threads from people's clothing or bandages that got stuck in scabbed skin. The disease is a fairly rare complaint that affects mostly middle-aged white women, studies suggest.

Scientists have tried for years to find out what might cause the symptoms of Morgellons, but nothing definitive has been found.

In one study, researchers at the Centers for Disease Control and Prevention looked at 115 people who reported having skin problems such asfibers or materials coming out of lesions in their skin, or "disturbing skin sensations."

But the researchers found no medical condition or infection that could explain the complaints, according to the results published in 2012 in the journal PLOS ONE. Instead, they concluded that symptoms of this condition resembled those of people with certain mental health conditions who believe they are infested with parasites, a condition known as delusional parasitosis.

If Morgellons is indeed related to a psychiatric condition, drug use may be a contributing factor, the researchers said. In the hair samples in 50 percent of patients in the study, the researchers found evidence of the use of drugs such as marijuana, amphetamines and benzodiazepines (which are used to treat people with anxiety and insomnia).

A study published in 2013 in the journal Clinical, Cosmetic and Investigational Dermatology, linked the condition with a tickborne type of bacteria called spirochaetes. But not much research supports this finding, or any other infectious cause.

But regardless of what may cause the unusual symptoms of Morgellons, the condition lowers the quality of life for Mitchell and others who say they have it.

It's not clear exactly what led to the singer's hospitalization. She underwent a surgical procedure at the hospital and is still in intensive care, but her assistants said she is "awake and in good spirits," TMZ reported.