One day stars are worshipped as gods...the next they encounter weakness in themselves and realize they are just human. Very few WOULDN'T experience mood swings.
In fact, a society ruled by secular humanism will, of course, be a society where bi-polarism is everywhere. Society teaches we are all-powerful, but our nature tells us we are not.
Atheist Russia had all kinds of "mental institutions". As socialism creeps forward in the US, we have our share of mind drugs and treatments as well.
People are born with Bi-Polar disorder.