The 42-year-old was suffering from vestibular migraines, her rep said in a statement, an unusual condition that creates the sensation of vertigo.
But Jackson is now receiving treatmet – and she's anxious to get back on stage.
"[Janet is] a world-class entertainer and needs to be at the top of her game to give her fans the show they expect," manager Kenneth Crear said in the statement. "She's feeling much better and is ready to hit the road again."
She is scheduled to resume her Rock Witchu Tour Wednesday night at the Verizon Center in Washington, D.C.
Jackson's show at Madison Square Garden, originally slated for Thursday, has been rescheduled for Nov. 1.
New dates for the other postponed concerts are being worked out and will be announced shortly, her rep said.