He had a severe benzo addiction and rather than going through the normal treatment of tapering off use, he opted for an experimental treatment offered in Russia where he was instead placed in a medically induced coma to avoid the worst of the withdrawals. This had other side effects though and he later described having to relearn basic motor functions after being awoken, so who knows what else that did to him.
His chemistry was messed up and he couldn't do a standard detox, the Russia place (sounded shady as f from his daughter retelling it) was the only place that would do this experimental way. ( Or even attempt it)
I think anyone who puts themselves into a coma because it's easier than fighting addiction has no room to scold me on my life choices, he was always stupid