TMZ: Craig Mack knew he was dying, at least for several months, from congestive heart failure ... according to his close friend, Erick Sermon.
The "Flava in Ya Ear" rapper had only 25% of his heart working in his final months... The coroner would only say Craig had died of natural causes.
Erick says Craig maintained his personality, though ... they eventually hooked up and even recorded some music, and shot a documentary before he died.
See more of this story via TMZ.
video via instagram.