Well I can now some what understand his motives... though years of cocaine abuse sometimes leads to this.

Robin Williams’ wife revealed Thursday that the actor was struggling with the early stages of Parkinson’s disease as well as deep depression and maintaining his sobriety.
“Robin’s sobriety was intact and he was brave as he struggled with his own battles of depression, anxiety as well as early stages of Parkinson’s Disease, which he was not yet ready to share publicly,” Susan Schneider said in a statement released by Williams’ publicist.

[link to pagesix.com]

Cocaine's influence
[link to www.sciencedaily.com]

The study's findings are important because there are currently more than 2 million cocaine abusers in the US today, the researchers said. Many individuals who abused the drug during the height of the cocaine abuse epidemic of the 1970s and 1980s are now entering their older years, when symptoms of PD are likely to emerge.