Fentanyl overdoses can make you feel like time is slowed down, like your heart is not beating barely at all, while at the same you struggle to breathe. It is a terrifying experience.
That he had a heart attack and/or struggled to breathe while overdosing on fentanyl is no shocker. Especially when combined with his heart condition and all the other drugs in his system that might have been potentiating it.
He was high off his ass while trying to pass off fake money at a store. He was not trying to sort his life out. It is possible that he did not intentionally take fentanyl, that maybe it was mixed in with some other drug he did choose to take. There have been many cases of that. Prince, for example.