"The first couple times it was difficult," Hetfield confessed, "and there are certain scenes in the film that will always be difficult."
The film chronicles the troubled making of Metallica's last album, 2003's "St. Anger," including the departure of bassist Jason Newsted, Hetfield's stint in rehab and intense sessions therapist Phil Towle conducted with the group.
"The fighting scenes, they're always pretty difficult," Hetfield said. "They always tend to get your heart pumping again, 'cause that makes sense 'cause it pushes a certain button in me and everyone's got those buttons."
The "Some Kind of Monster" DVD adds 28 deleted scenes to the 140-minute film.
Metallica is currently taking time off but plans to work on a new album later this year.