Died in sleep pregablin

The father of my son went to sleep after taking pregablin and alcohol. He never woke up. Not sure how accurate this statement is but I know he was taking pregablin leading up to his death. Found with vomit around his mouth unknown whether he choked on this or not as postmortem results aren’t known as well as no cause of death. Awaiting toxicology results also. How does this even happen? Did he just stop breathing? Another version is he just drank alcohol and went to sleep and took no drugs and died? Conflicting information. I just need answers. Wouldn’t they know how he died after postmortem?