(CNN) - Solange Knowles has canceled her New Year's Eve gig at the AfroPunk festival in South Africa, blaming health issues.
The singer/DJ, who performs under her first name, revealed Wednesday in an Instagram post that she has been dealing with an illness.
"The past five months I have been quietly treating, and working through an Autonomic Disorder," she wrote. "It [sic] been a journey that hasn't been easy on me."
According to the Mayo Clinic, autonomic nerve disorders affect the autonomic nervous system, which controls a person's involuntary functions.
"Symptoms are wide-ranging and can include problems with the regulation of heart rate, blood pressure, body temperature, perspiration, and bowel and bladder functions," says the Mayo Clinic's website. Other symptoms include fatigue, lightheadedness, feeling faint or passing out, weakness and cognitive impairment.
Knowles, 31, younger sister of superstar Beyoncé, had been set to headline the festival in Johannesburg, which will run from December 30 to January 1.
The singer wrote on Instagram that she had struggled with finding the words to describe her condition.
"However it's so important to me for the people in South Africa, a place that has tremendous meaning to me and that has given me SO SO MUCH, to know why I won't be performing at Afro Punk this NYE," she wrote.
"Sometimes I feel cool, and other times not so cool at all," she said of living with the disorder. "It's a complicated diagnoses [sic], and I'm still learning so much myself, but right now, my doctors are not clearing me for such an extended lengthy flight, and doing a rigorous show right after."
Solange vowed to return for a concert in Johannesburg later in 2018.
In a Facebook post Thursday, the AfroPunk festival said it only learned "within the last day" that Solange was canceling her appearance.
"We value her as an artist and above all as a human being and understand that her health is paramount," the festival said in a statement. "Though we have worked with Solange on multiple festivals this year, we were not among the few who were aware that she has been privately dealing with this diagnosis. We believe and trust her commitment to grace the 2018 AFROPUNK Joburg stage."
In her post Solange thanked AfroPunk and organizers of other festivals, as well as friends and family who knew of her diagnosis and kept it quiet.
The singer vowed to do better with her self-care in 2018 and had words of gratitude for her fans.
"Performing this record and experiencing the energy exchange with you guys has been astounding, and I'm so excited about continuing to do the work I feel so absolutely humbled and appreciative to be doing next year," she wrote. "It gives me life."