Mariah Carey is suffering from insomnia.

The singer is struggling to get to sleep at night and has taken to watching her husband Nick Cannon doze peacefully while she is wide awake.

She wrote on her Twitter page: "I just finished working out. Whooo! Quite naturally, 'its 5am and I still can't sleep'(sung like 'crybaby' from 'Rainbow' 99)lol Who's up?

"Nick is too cute when he's sleep! I wish he didn't have to work tomorrow so he could help me sleep all day and I could sing all nite (sic)!" Mariah is not the only celebrity to suffer from sleepless nights.

Robbie Williams often finds it difficult to drop off, especially after a live show. A source said: "Rob has a problem sleeping and it's very hard for him to know what to do after he has performed."

Brad Pitt - who has six children with partner Angelina Jolie - recently revealed fatherhood has ruined his sleep.

He said: "Being a parent is the one thing that really keeps you up at night. Angelina and I have to be smart and prepared, and we are more responsible when it comes to the areas we decide to visit."

Salma Hayek also revealed that after having her daughter Valentina Paloma in September 2007, she didn't sleep for six months.

She said: "I don't even remember what my life was like before. I can tell you that I don't sleep. This is a cliche but it's true. I haven't slept in the last six months.

"The blessing of having a healthy child, I think is the best thing that can happen to anyone."