Solange Knowles announced on Instagram Dec. 27 that she has an autonomic disorder, sharing a diagnosis of a type of condition that is linked to automatic and involuntary bodily functions

The singer made the statement while explaining that she would not be performing at the Afropunk Fest in South Africa on New Year’s Eve as planned. Knowles said she is “quietly treating and working through an autonomic disorder.”

“It [has] been a journey that hasn’t been easy on me,” she wrote. “Sometimes I feel cool, and other times not so cool at all. It’s a complicated [diagnosis], 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.”

She also promised to perform with Afropunk at a later date.

The singer had previously canceled appearances at two other concerts this year due to a medical condition, according to Entertainment Weekly.

While Knowles, 31, did not reveal which specific autonomic disorder she has, the group of conditions affect the involuntary functions of the body — things within the realm of the autonomic nervous system. Those functions can include digestion and the constriction or dilation of blood vessels, which controls circulation.

The Mayo Clinic gives examples of autonomic disorders — a group of conditions that is also known as dysautonomia — such as orthostatic hypotension, in which blood pressure drops upon standing; erectile dysfunction; and neurogenic bowel, which can occur after a spinal injury and affects a person’s ability to control their bowel movements.

Because there are different kinds of autonomic disorders, they can create lots of different symptoms. According to the Mayo Clinic, some people get symptoms like abnormal blood pressure, heart rate or body temperature, bowel or bladder dysfunction, fatigue, lightheadedness and fainting.

The U.S. National Institute of Neurological Disorders and Stroke notes that autonomic disorders can be a person’s primary health issue, or they can occur as a result of another health problem. For example, they can be associated with Parkinson’s disease or another degenerative neurological disease.