What's Happening With Ms. Jackson?

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.

Then, over the weekend, her publicist said in an e-mail that after Jackson arrived in Greensboro, N.C., hoping to perform on Saturday, a local doctor advised her not to go on stage after it became "evident" she had not fully recovered. Jackson postponed Saturday's show, one on Sunday in Atlanta and a third scheduled for today in Fort Lauderdale.

Jackson's reps have not disclosed the illness she's "recuperating" from, leaving the celebrity media to speculate.

But Ian Drew, a senior editor at US Weekly, believes it may be nothing more than exhaustion. "She hasn't toured for a while," he said. "People are putting a negative spin on things. I think it's very undeserved. This last record was one of her better records ever. But it's always hard with these kind of legendary pop stars. They become trapped in their persona and it's really hard to get new fans. It's about keeping the core group. She risks abandoning them if she changes too much."

Jackson has also taken a few shots lately for her weight and personal life. Some stories have hinted that her weight is creeping up again. Jackson infamously dropped 60 pounds in 2006 and posed for US Weekly covers, flashing her famous abs again.

Drew says she still looks great. "She's come out and said when she's not touring, she is less likely to exercise as much," he said. "But we're not seeing these huge numbers."

The self-confessed yo-yo dieter is writing a book about her battle of the bulge, that is scheduled to come out by year's end.

Last month, the New York Post reported that Jackson's longtime boyfriend Jermaine Dupri, head of Island Def Jam, had too much of a good time on his 36th birthday and vomited in Jackson's lap. Jackson fled from the restaurant in her chauffeured Maybach, according to the Post.

"I highly doubt that that happened," Drew said. "The thing about Janet is she is very loyal. She tends to stick with people, her dancers, her hairdresser. She's always in a relationship. I think she and Jermaine are a great couple. They're very solid."

Jackson's career is another matter. "I think she should just do something totally different," Phoenix, the former family spokesman, said. "She should just act. You can grow old with acting."

"I would personally like to see her do something a little bit surprising, like starting her own label and doing something unpredictable," said Cohen, who thinks she's off to a good start by leaving her old label. "Would it be so crazy to bring Michael on stage each night? He needs something like that. And so does she."