Robin Williams was in the early stages of Parkinson's disease when he took his own life, a statement from his wife said.
Susan Schneider revealed her husband was "not yet ready to share publicly" his battle with the disease.
She added the actor, who has famously suffered addictions to drugs and alcohol, was also sober at the time.
Robin Williams' daughter has left social media after receiving abusive messages in the wake of her father's death.
Radio station talkSPORT has apologised after presenter Alan Brazil said he lacked sympathy for actor Robin Williams, who took his own life.
He played a wide range of roles but Robin Williams captured the hearts of millions with his performances.