The former gangster witnessed dozens of murders during his 25 years working for the Mafia in New York, and admits he often "cracked heads" with a baseball bat during underworld clashes.
Hill turned informer in 1980 and has since tried to rebuild his life - but he is still tortured by his past and is plagued by nightmares about violent 'hits'.
He tells GQ magazine, "You had to grin and bear it to be part of the crew. It was a lot of f**king play acting. When (a murder) was over, I'd puke my guts out... I don't really want to talk about that s**t. I really don't. I wake up in the night sometimes, screaming. I wet myself, I scream so hard. Women and children. Horrible s**t."
Hill's story was told in Martin Scorsese's 1990 classic Goodfellas, with Ray Liotta taking the role of Hill.