The Blue Monday singer twice put his close pal into a trance when they worked together in Joy Division in a bid to help the troubled frontman deal with his personal problems.
However, the sessions failed to bring Curtis out of his slump and after he hanged himself in May, 1980, Sumner vowed not to mess with hypnotism again.
He tells Uncut magazine, "I read a book on hypnotism, before I knew Ian... Then I read a book about hypnotic regression - a couple of books, actually. I tried it out on Ian and it worked. I did it twice actually, once at rehearsals and once at my house. I just thought it may help him in some way... I thought I'd give it a go. It didn't sort him out, though. I never did it to anyone else after what happened to Ian, because it made me a bit paranoid about it."