David Harewood was forced into a psychiatric hospital in 1988.
The 'Homeland' star has revealed he was sectioned under the mental health act 30 years ago and forced to spend time on a monitored ward at the Whittington Hospital in Archway, North London, for his own safety after his behaviour became "erratic."
Speaking to the Daily Mirror newspaper, the 52-year-old actor said: "I got to the stage where my behaviour was deemed to be, I wouldn't say dangerous, but I didn't care.
"I remember bits of it. I remember friends coming to see me and the odd moment of lucidity but I was very heavily sedated. Most of it I was asleep for, to be honest.
"I had absolutely no idea where I was or why I was there or how long I was in there. I can remember at one point thinking, 'Why can't I get out of these doors?'
"I can remember trying to get out and thinking, 'Why are these doors locked?' and then people coming towards me and helping me back into bed. And I was thinking, 'Why can't I go home?' and just being very confused.
"I didn't really know where I was and why I was there. And in the 30 years since no one has actually been able to tell me exactly what happened."
The 'Supergirl' star recalled a moment in the hospital when he convinced himself that legendary poet William Shakespeare - who died in 1616 - was talking to him.
He explained: "I remember just lying there and I heard somebody talking Shakespeare and even in my drug-addled brain I thought, 'I recognise that.'
"And I sat up and looked for him, and looked around and he was wandering the ward. And I'm sure it was, it was Shakespeare. And for some reason it made me feel better.
"It comforted me because I didn't know who I was. But I knew Shakespeare when I heard it. Then I remember drifting off to sleep thinking, 'No, it's OK, everything's OK, I'm all right,' because it brought me comfort to hear something that I was familiar with, because everything around me was not."
David will look into mental health more for his forthcoming documentary 'David Harewood: My Psychosis and Me' on BBC.