Since last week, when she became "suddenly ill" and had to be hospitalized, Janet Jackson has cancelled six concerts in what some were calling her comeback tour.
Is it vertigo, as her brother Randy reportedly said last week, or is Janet suffering from an ailment more common to aging '90s pop stars: a mid-life career slump?
At 42, Jackson is certainly not the only middle-age female pop star rocking the concert circuit. Just look at Madonna, 50, whose "Sticky and Sweet" tour is virtually sold out and getting rave reviews. Or Tina Turner, who is about to embark on another tour at nearly age 69.
Why does Jackson, seemingly the most stable of the Jackson clan, appear to be losing her footing?
"Her music hasn't really evolved as she has aged as a person, said Jonathan Cohen, a senior editor at Billboard magazine. "She's still doing the sex kitten thing, which, at 42, really isn't believable."
Pearl Jr., who runs the Michael Jackson fan site MichaelJacksonInsider.com, spoke to Randy last Tuesday, she said in an e-mail to ABCNews.com. He told her, "Janet is doing OK, she suffers from vertigo," which she posted on her web site.
Vertigo is a disturbance of the equilibrium that causes dizziness or the sensation of falling while the body is actually stationary.
But the former Jackson family spokesman known only as Phoenix is skeptical of reports of vertigo, adding that Randy has been out of touch with his sister.
"It's not really Janet, it's the promoter," said Phoenix, who stays in contact with the family and fronts a Jackson tribute band called the "Dancing Machine Revue."
"They are pulling out due to bad ticket sales. Janet might have been one of the greatest pop icons in her time. But Janet Jackson, at 42 years old, does not have the same appeal as in '89 with 'Rhythm Nation.' Other artists took that throne -- Ashanti and Beyonce. This is what you call a publicity stunt."
Jackson has not had a great year. Her album "Discipline" was meant to be something of a comeback after her last two albums tanked, following the 2004 Superbowl, in which Justin Timberlake accidentally exposed her bare breast during a wardrobe malfunction. Released in February, "Discipline," considered to be one her best albums in years, has not even sold half a million copies.
"It was dead on arrival," Cohen said.
Then, last month, she announced she was parting ways with the album's label, Island Def Jam Records, after only 14 months. In a video blog for rap-up.com, Jackson's longtime collaborator Rodney Jerkins said, "We didn't get the support from the record company. [Janet] felt like it wasn't pushed. I felt like it wasn't pushed correctly. She just didn't get her just due as an artist of that magnitude."
And now the "Rock Witchu" tour, Jackson's first North American tour in seven years, appears to be in peril. While Jackson has not completely filled the arenas where she has performed, with six shows reporting earnings so far, she had drawn 53,000 fans and grossed nearly $6 million in ticket sales, according to Billboard.
What's less clear is how the show will go on with Jackson's undisclosed illness.
Last Monday, Jackson became "suddenly ill" and was hospitalized in Montreal shortly after she arrived for a show. She cancelled concerts in Boston and Philadelphia on Wednesday and Thursday.