Claire Foy suffered a breakdown after landing the lead in the BBC period drama Little Dorrit.

The Crown star was 23 at the time and tells Porter Edit magazine she suddenly discovered her world had turned upside down - and she just couldn't cope.

"I didn’t sleep or eat for a month," she tells the publication. "It was awful. My life had changed. I felt overwhelmed.

"I was on stage at the time and working, and I’d just got a really big job. I just couldn't cope."

Claire admits becoming a mum in 2015 when her daughter Ivy Rose was born helped her put a lot of things in perspective, but she has given up on trying to find permanent happiness.

"A long time ago, I gave up on the idea of happiness," she adds. "I think you can be incredibly, deliriously happy one minute, and be miserable the next...

"I’ve realised that my life is quite dramatic, and that’s OK. I’m really happy, but... I'm not sorted, at all. I don’t expect any moment to last."

"Having her (daughter) made me think, 'You need to sort your life out'," she adds. "I just didn’t have to live like that. It was unbearable. I was sick of myself."

The 34 year old recently confessed she's plagued by anxiety, telling The Guardian's Weekend magazine, "When you have anxiety, you have anxiety about - I don't know - crossing the road... It's not related to anything that would seem logical. It's purely about that feeling in the pit of your stomach, and the feeling that you can't, because you're 'this' or you're 'that'. It's my mind working at a thousand beats a second, and running away with a thought."

Claire reveals she developed anxiety as a child as a "tool to survive" after her parents separated when she was eight. "Make everybody happy. Never be angry. Be really sweet and well-behaved," was her childhood response to the heartbreaking family split.

When asked if her growing success had increased her anxiety levels, she laughed: "Oh, God. It definitely magnified when I started doing this. Exploded. Yeah."

But therapy has helped over the years: "It's still there, but I guess I don't believe it so much any more. I used to think that this was my lot in life, to be anxious. And that I would struggle and struggle and struggle with it, and that it would make me quite miserable... But now I'm able to disassociate myself from it more," Claire added.