The comedy actress told the BBC Radio 4 programme she felt it was “all a bit too much” a year ago, but was now feeling “happier and more confident”.
The TV star, who will appear in a Call the Midwife special on Christmas Day and Gangsta Granny on Boxing Day also spoke about her father’s “lucky” survival during the Falklands War.
Her episode of Desert Island Discs will be broadcast at 11:15 GMT today.
She told presenter Kirsty Young her worries surfaced when she was filming a documentary about her hero Eric Morecambe.
‘Fine as a woman’
“I think I got to a point a year ago possibly when it was all a bit too much,” she said.
She said she was “quite lonely” and was “struggling” at the time of filming because she was wondering if her chosen career was worthwhile.
“So that was the key question I would have asked Eric and I hoped he would say ‘Yes, it was worth it’,” she said, choosing the Morecambe and Wise theme Bring Me Sunshine as one of the discs she would take to a desert island.
“Then you find ways to manage your life that mean you’re not in that place, which I’m not now, and I’m much happier and more confident and celebratory about what I’ve achieved, and feel it’s fine as a woman to be confident and pat myself on the back.”
Among her other music selections for the programme was a Mozart piano concerto her father, David Hart Dyke, listened to while serving in the Falklands War.
He was the commanding officer of HMS Coventry when it was sunk by the Argentine air force, killing 19 crew, and she said he was “lucky to survive”.
“He didn’t speak at all when he got back but he put everything on tape and then when I was in my early 20s he allowed me to type them all up, which was amazing and quite emotional listening to his voice going through it so close to the event,” she said.
She said her father was “absolutely convinced he was going to die” but managed to get off the ship, which “went down in 15 minutes”.
The Call the Midwife Christmas special will be broadcast at 18:15 GMT
Gangsta Granny is on Boxing Day at 18.05 GMT