I suspect he was hopelessly losing his battle with depression that had dogged him for so long and probably drove him to drug use. Then having attempted to whip the drug habit, the depression came back to an even worse degree. I hope that isn't regarded as a cruel assumption since I admired him a great deal for his ability to convey deep human emotion as well as absolute over the top comedy. When he played a serious role, such as in Mrs. Doubtfire, it really made you understand and believe how it felt to be in that situation and it all seemed so real that you forgot that he was also an outstanding comic.
Good Morning, Vietnam,
Just three of my absolute favourite RW movies, but there re more.
RW brought so much life and positive energy to virtually everything he did as an actor and entertainer.
Thank you, Robin Williams, for bring us so much joy and cherished memories, by vehicle of your greatest works as a performer and professional actor.