Entertainment legend Garry McDonald is a man on a mission. He is determined to educate the public about a mental health problem that once brought him unstuck.

The performer has suffered from anxiety since his 20s but never understood his condition until it triggered a major and very public breakdown in the 1990s.

Despite an increased awareness in the community about mental health and depression, "anxiety disorders are just never cottoned on to," McDonald told Australian Story.

Garry McDonald made a name for himself in the early 1970s, first in the comedy sketch show Aunty Jack, then with his comic character Norman Gunston, a gormless talk show host from Wollongong who embarrassed and entertained Australians as he interviewed the world's hottest celebrities.

Theatre director Peter Evans, who has worked with McDonald, says performing Norman is a risky business.

"The kind of livewire act that it is to do that sort of comedy, a lot of that's improvised. It would have to be incredibly stressful to be working at that level in those situations," he said.

The more successful Norman became, the more McDonald doubted himself.

"My mind would always be telling me I was going to make a fool of myself and people ... were looking at me and saying, 'Oh, God, that show he did last night was dreadful'."

Despite the nerves, the actor went on to star in the hit TV series Mother and Son but when he relaunched the Norman Gunston Show in 1993 he cracked under the pressure and the show was cancelled.

"I was mortified that I was putting people out of work," said McDonald.

"But there was nothing I could do. I was a basket case."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 48 seconds 48 s Norman Gunston interviews Muhammad Ali

Once the actor was diagnosed with anxiety, and related depression, he began treatment in the form of cognitive behaviour therapy.

This changed his life and the actor has been busy ever since, on stage, film and in TV dramas including Offspring and Rake.

A member of Beyond Blue's board for 10 years, McDonald campaigned to help reduce the stigma of anxiety and to spread the that word it is treatable.

He calls for more people, in particular performers, to come out with their personal stories.

"There's a terrible, terrible need for people to talk about anxiety," he said.

The semi-retired actor will not call himself cured, preferring to say he "manages" his anxiety.

"It's no great strain," he adds.

You can see All in the Mind on Australian Story at 8:00pm tonight on ABC.