The Arya Stark actor said: "I had a traumatic relationship with my dad and ever since I can remember I have struggled sleeping."
Going into more detail, Williams added: "It met its peak and when I was at school I was taken by a teacher to the staff room. She asked me what had happened. She asked me if I ate breakfast I said 'no', and asked if I did most mornings. I said 'no'. They were asking the right questions."
Williams' mother "escaped" the relationship with her father when the actor was just four months old.
The Pistol star also said: "I think a lot of the traumatic things that were happening, I didn’t realise they were wrong."
Williams admitted that she is able to channel her emotions through her work: "I’ve known how that feels and its hugely influenced, I get to access all of that confusion and pain in my job, and really feel it in every fibre of my being… it’s all pretend but the emotion is real…it all just came to the surface."
She added: "I feel now there is some sort of closure to it, where the journey may help other people where as before it was just pain, pain pain and pain."
Williams was cast on Game of Thrones as Arya Stark at just aged 12 and appeared on every season of the hit fantasy show, becoming a fan favourite character.
For her portrayal of Arya, Williams was nominated for two Emmy Awards. She has also gained acclaim for her performances in The Falling and Two Weeks to Live.
Watch below: Maisie Williams' guide to Pistol's punk makeup.