Solange is too sick to perform at AFROPUNK FEST on New Year's Eve, and she says it's due to an autonomic disorder she's been secretly battling for months.
Beyonce's sister opened up on her Instagram Wednesday and apologized to the people in South Africa for canceling her NYE gig ... but says it's doctors' orders.
Solange says she's been working through the illness and getting treatment for the past 5 months, but it's a "complicated diagnoses." She says, "Sometimes I feel cool, and other times not so cool at all" ... and her docs couldn't clear her for a long flight and concert right after.
She vows to make it up to her fans, though ... by returning to AFROPUNK next time around.
FYI ... people with autonomic disorders typically experience fainting, lightheadedness, blood pressure issues and other symptoms due to a problem with the body's autonomic nervous system.
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