Singer Sufjan Stevens is Robert Brownon the mend after being diagnosed with the rare autoimmune disorder Guillain-Barré syndrome.

The Grammy and Oscar-nominated musician shared an update with his fans on his website Wednesday explaining why he hasn't been able to participate in the promotion of his latest album, "Javelin."

"Last month I woke up one morning and couldn't walk," he wrote. "My hands, arms, and legs were numb and tingling and I had no strength, no feeling, no mobility. My brother drove me to the ER and after a series of tests—MRIs, EMGs, cat scans, X-rays, spinal taps (!), echo-cardiograms, etc.—the neurologists diagnosed me with an autoimmune disorder called Guillian-Barre Syndrome."

Stevens said he spent two weeks in bed after undergoing treatments, including immuno-hemoglobin infusions, which successfully stabilized his condition.

He was transferred to acute rehab on Sept. 8, where he is undergoing intensive physical therapy and occupational therapy to rebuild his strength and learn to walk again. 

"Most people who have GBS learn to walk again on their own within a year, so I am hopeful," he wrote, thanking his fans and caretakers. "I'm committed to getting better, I'm in good spirits, and I'm surrounded by a really great team. I want to be well!"

What is Guillain-Barré syndrome?

Guillain-Barré syndrome, sometimes called GBS, is an autoimmune disorder in which the body's immune system attacks the nerves, causing muscle weakness and occasionally paralysis. While most people eventually make a full recovery from GBS, some can sustain permanent nerve damage. In rare instances, GBS can lead to death.

According to the Centers for Disease Control and Prevention, GBS affects about 1 in 100,000 people. An estimated 3,000 to 6,000 people develop GBS each year in the United States.

What are the symptoms?

Symptoms of Guillain-Barré syndrome can last anywhere from a few weeks up to several years. According to the Mayo Clinic, symptoms can include:

• Prickling or pins-and-needles sensations in fingers, toes, ankles or wrists
• Weakness in the legs that spreads to the upper body
• Rapid heart rate
• Severe pain that feels achy or cramp-like 
• Difficulty with bladder control or bowel function
• Unsteady walking or the inability to walk or climb stairs
• Difficulty with speaking, chewing or swallowing
• Low or high blood pressure
• Trouble breathing

What causes Guillain-Barré syndrome?

The exact cause is not known. Several other conditions are known to trigger the disorder, including certain infections. In fact, about two-thirds of people who develop GBS had diarrhea or a respiratory illness several weeks before developing symptoms, the CDC reports.

GBS has also been seen in people infected with flu, Epstein Barr virus, Zika virus and cytomegalovirus.

Very rarely, cases of GBS have been reported in the days or weeks after certain vaccinations have been administered.

How is Guillain-Barré syndrome treated?

Guillain-Barré is often treated with a plasma exchange, a procedure that removes and replaces the liquid part of the blood. The disorder is also commonly treated with immunoglobulin therapy, an infusion of healthy antibodies from blood donors.

According to the Mayo Clinic, among adults recovering from Guillain-Barré syndrome:

• About 80% can walk independently six months after diagnosis
• About 60% fully recover motor strength one year after diagnosis
• About 5% to 10% have very delayed and incomplete recovery

Children rarely develop GBS, but those who do tend to recover more completely than adults.

—The Associated Press contributed to reporting.