Jim Parsons was the face of The Big Bang Theory for 12 years – but it took a serious toll on him mentally, leaving him “miserable” and “stressed”.The actor, 53, played Sheldon Cooper from 2007 to 2019 in the hit CBS sitcom, which launched the actor to global fame – and while he acknowledges that he experienced “some of the best moments of my life” during that time, Parsons said he “looks back now and realises that there were many ways” he was miserable.“I was not happy,” he told YouTube podcast All Out with Jon Dean. “I was stressed. I felt that there were so many plates I was supposed to be keeping in the air and that the success and the good things of life that were happening were only due to this overworking, discipline and whatever.”Jim Parsons said he wouldn’t relive ‘Big Bang Theory’ days if given the choice (Getty Images for Tony Awards Pro)He continued: “Maybe, to a degree, that was true. I don’t know. I can’t say because that’s how I was.”Parsons said he would not return to those days for “any amount of money” as the work ethic translated into “obsessive behaviour, basically”.“Yes, I was disciplined. Yes, I had a good work ethic, but a lot of it was because it was kind of OCD in nature. I had a list of things basically in my head that I had to get done in order to be comfortable and know that I could do my job right, which I don’t think was true.”He also reflected on the legacy of Sheldon, revealing that his relationship with the character is “evolving” and “getting better all the time”.The Big Bang Theory became a huge hit for CBS and led to its lead stars, including Kaley Cuoco, Kunal Nayyar and Simon Helberg, becoming the highest-paid stars on TV.Jim Parsons as Sheldon Cooper in ‘The Big Bang Theory’ (CBS)Watch Apple TV+ free for 7 dayNew subscribers only. £9.99/mo. after free trial. Plan auto-renews until cancelled.Try for freeADVERTISEMENT. If you sign up to this service we will earn commission. This revenue helps to fund journalism across The Independent.Watch Apple TV+ free for 7 dayNew subscribers only. £9.99/mo. after free trial. Plan auto-renews until cancelled.Try for freeADVERTISEMENT. If you sign up to this service we will earn commission. This revenue helps to fund journalism across The Independent.According to Entertainment Weekly, it ended because Parsons turned down $50m (£37.1m) to return for a 13th and 14th run.When the show’s final season was announced, he expressed “intense gratitude” for the crew, writers and his fellow castmates, writing: “I will miss all of you and all of this more than I can say and more than I can know at this time.”A second spin-off to the show is set to begin next month. Stuart Fails to Save the Universe focuses on Stuart Bloom, the owner of the comic book store frequented by Big Bang Theory characters Sheldon and Leonard (Johnny Galecki). The new show sees him break a device Sheldon and Leonard built, which leads to a multiverse armageddon.The new HBO Max series will also build upon the budding romance between Stuart – played by Kevin Sussman – and Denise, played by returning cast member Lauren Lapkus. Also joining for the adventure is geologist Bert (Brian Posehn) and quantum physicist Barry Kripke, played by John Ross Bowie.Young Sheldon became another hit for CBS, lasting for seven seasons from 2017 to 2024. When the show came to an end, executive producer Steve Holland stated: “This is the right time for this story to come to an end.”Since leaving The Big Bang Theory, Parsons has appeared in the film Extremely Wicked, Shockingly Evil and Vile (2019), The Boys in the Band (2020) and Spoiler Alert (2022).