Rihanna has reportedly been surviving on two hours' sleep a night.
The Bajan singer was hospitalised with flu earlier this month, said to be caused by her hectic schedule and love of partying.
Rihanna has previously spoken of being brought to tears by how busy she is with work - she's been promoting her first movie Battleship this year and has released an album, while her last tour finished in December.
However, friends worry she hasn't used her downtime to her best advantage.
"Instead of resting, she parties and goes for days on as little as two hours sleep," a source told Look magazine.
The 24-year-old star was also taken to a medical centre last November and those close to her are apparently begging her to take better care of her health.
"Even with an IV in her arm, Rihanna thinks she's invincible," the insider added. "Those close to her have begged her to go to rehab but she's told them she doesn't need help."
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