The Dangerous Method actor, who plays Sigmund Freud in the psychological drama, said that he believes therapy sessions can be helpful for everyone and also prevent issues from manifesting in negative ways.
"I only had one experience when I was about 24. I went for a short time. For me, it was helpful," Mortensen explained in a new interview with The Huffington Post.
"I think it's a great idea - the idea that you can go and confess everything, your deepest fears, your insecurities, your strangest thoughts to someone and know that it won't go any farther than that room. If you don't find some way to discuss or recognise what's going on inside you, it can come out in other ways that are self-destructive."
Mortensen went on to say that he was surprised to learn more about Freud's personality, adding: "He was very engaging and very funny, also sometimes quite self-deprecating. He was the sort of person who tells you a joke, and it might be quite subtle and not everyone would get he was telling a joke.
"He did enjoy silly humour. He was also an admirer of Mark Twain. The two met, and they smoked cigars and cracked jokes."
A Dangerous Method, which also stars Keira Knightley and Michael Fassbender, is released in the UK on February 10.
Watch the trailer for A Dangerous Method below: