The British actor has played Jon Snow in HBO’s fantasy behemoth since 2011 and will pull on his famous fur cape for the final time when season eight airs in April.
Harington was largely unknown when he first appeared in Game Of Thrones but is now one of the most recognisable faces on TV thanks to the show.
Speaking to Variety, the 32-year-old admitted to feeling the strain when Jon’s prominence in the show steadily increased and his own fame rocketed.
He said: “It wasn’t a very good time in my life. I felt I had to feel that I was the most fortunate person in the world, when actually, I felt very vulnerable.
“I had a shaky time in my life around there – like I think a lot of people do in their 20s. That was a time when I started therapy, and started talking to people. I had felt very unsafe, and I wasn’t talking to anyone.
“I had to feel very grateful for what I have, but I felt incredibly concerned about whether I could even f***ing act.”
The eighth and final season of Game Of Thrones arrives in April and Harington said US TV Network HBO have not rested on their laurels with the series’ previous success and have instead went “balls out”.
He added: “They could have easily set the same budget as they did for season seven, but they went bigger.”
And while the series’ end is being kept tightly under wraps by HBO, Harington, who met his wife Rose Leslie on Game Of Thrones, did offer fans a clue as to the fate of Jon.
Read more: Game of Thrones S8 episode lengths
“The end of Jon’s journey, whatever that may be… I was satisfied with how his story ended”, he said.
Game of Thrones returns to Sky Atlantic for its final season on 15 April. You can watch the first seven seasons on NOW TV.
Reporting by PA