The 'Luther' star leapt off stage to help Amanda Bilington when he saw she was having a fit in the audience at the Upper Campfield Market in Manchester during the preview of his new production 'Tree' on Wednesday (03.07.19).
The 33-year-old theatre-goer - who suffers from regular seizures due to an undiagnosed condition - didn't realise the 46-year-old actor was standing by her side until she regained consciousness a little while later and he continued to stay with her until the paramedics arrived to take over her care.
Mrs Bilington told the Daily Mirror newspaper: "I would love to thank him personally, but doubt I will cross paths with him, he's very famous."
Meanwhile, although Idris is busy with the play at the moment, the 'Mountain Between Us' actor - who is married to Sabrina Dhowre and has children Isan, 17, and five-year-old Winston from previous relationships - needs "balance" because he wants to spend as much time as possible with his loved ones.
He said recently: "Everything's a balance in life. I have to do the work, because it's a popular time for me, and it's best to have that. But also: I'm madly in love with my wife and my children.
"At home, I'm not famous: I'm me. And to my team and my family and the people that I work with every day when we build what we build, we're not famous. You know what I mean? It's day one every day."
The handsome star wishes he could be more "obscure" but still have a successful career.
He explained: "Daniel Day-Lewis is an incredible actor but does not like to be in the public eye and manages to do the two. I can't do that. I wish I could. I wish I could just be obscure, and no one ever have to see me, and never have to do interviews, and still have the career that he has."