Kristen Stewart used to make herself ill if she wasn't in control.

The 25-year-old actress struggled to cope with her ''intense'' early success and was ''constantly anxious'' worrying about what could happen.

She said: ''Between ages 15 and 20, it was really intense. I was constantly anxious. I was kind of a control freak. If I didn't know how something was going to turn out, I would make myself ill, or just be locked up or inhibited in a way that was really debilitating.''

Kristen - who causes a scandal in 2012 when it emerged she had cheated on then-boyfriend Robert Pattinson with her 'Snow White and the Huntsman' director Robert Sanders - admitted she has become more ''feral'' and less concerned about her image in recent years.

She said: ''Lately, I've been doing less of the 'I'm sooooo sorry.' And more of the 'No. F**k. Jesus.'...

''Speaking very candidly, it was a really traumatic period in my early 20s that kick-started something in me that was a bit more feral.''

And the 'Twilight Saga' actress - who is rumoured to be dating her assistant Alicia Cargile - is ''proud'' she is learning to be a ''smarter and calmer'' person.

Speaking to America's Marie Claire magazine: ''I'm really proud that I am able to move forward and not fall into every mental crater. That's a new thing for me. Age has made me smarter and calmer. And it is f***ing awesome.''