"This type of extreme reaction can last from five to 27 days," her rep says of the singer's allergy to antibiotics

Credit: Jeff Kravitz/FilmMagic

When a celebrity falls ill unexpectedly, eyebrows are bound to be raised.

So when Miley Cyrus suddenly canceled two shows this week – citing a severe allergic reaction to antibiotics – there was some skepticism given her penchant for having a good time. But cynics be damned!

A rep for the singer, who is in the midst of her Bangerz Tour, clarified the singer’s condition – and its severity.

“Miley was suffering from a sinus infection during her tour in [North Carolina] a week ago,” the rep tells PEOPLE. After being prescribed the antibiotic cephalexin, she “suffered an extreme allergic reaction.”

“This type of extreme reaction can last from five to 27 days in these types of cases,” the rep says. “She will remain hospitalized and is under a doctor s care until we see some improvement in her condition and is asking for your compassion and privacy at this time.”

Cyrus, 21, who has been Tweeting from her hospital bed, “is devastated about missing shows and possibly disappointing her fans,” adds the rep.

Thursday morning she posted, “can’t quit crying i wanna go back on tour. im meant to be onstage performing for y’all…. not laying in a hospital bed.”

The singer has fought back at any naysayers who questioned her hospitalization and tour cancellations, Tweeting on Wednesday: “humans can b so selfish. If any1 thinks id rather b laying n a hospital bed than doing what I love on stage theyre LAME. Im miserable.”

Cyrus is no stranger to forging ahead in the face of personal setbacks. After her beloved dog Floyd died earlier this month, she continued her tour, giving an emotional onstage tribute to the deceased pooch.

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