Charlize Theron spent five days in hospital after laughing too hard at 'Borat'.

The 43-year-old actress revealed that whilst watching Sacha Baron Cohen's 2006 comedy film with a pre-existing neck condition, she laughed so much her ''neck locked up'' and after leaving the cinema in an ambulance, the 'Long Shot' star has never finished the movie as it's too much as a ''risk''.

Speaking on 'Late Night with Seth Meyers' she said: ''I went to go see 'Borat' I had a pre-existing injury in my neck - a herniated disk in my neck. A few of us went to go ... and halfway through that movie, I laughed so hard that my neck locked up. And, like, an ambulance had to take me to the hospital, and I was in the hospital for five days. I didn't finish the movie! I've never, like, fully finished the movie. It's a risk now!''

The 'Atomic Blonde' star also recalled a hilarious gift given to her by her pal Rihanna, who she shares the same publicist with.

Charlize confessed that the 'Work' hitmaker - who turned 31 in February - gifted her with a T-shirt with a birthday greeting from their publicist Amanda Silverman on the front, which stated Rihanna was her ''favourite client ever''.

The 'Monster' actress explained: ''A couple of months ago I got something in the mail, it was a T-shirt. Rihanna had made a T-shirt of the birthday greeting that my publicist gave her which literally was like, 'To my most favourite client ever.' And Rihanna wrote in the following email, 'I'm making a T-shirt of this and sending it to Charlize.'''