Thankfully she's feeling good enough to return to the road.

After postponing a string of concert dates due to illness, Janet Jackson is feeling well enough to resume her Rock Witchu tour -- and now, the pop star's reps are telling ET all about her previously unknown ailment.

Janet's reps tell us she was suffering from a rare form of migraine headache called vestibular migraine, which induces the sensation of vertigo.

The 42-year-old singing sensation is currently receiving treatment for the migraines and is "feeling much better and is ready to hit the road again to finish the tour," her reps tell us.

Janet's Rock Witchu tour resumes Wednesday night at the Verizon Center in Washington, D.C.