The death of beloved comedian Robin Williams has shocked so many of his fans and fellow comedians, with many struggling to understand how someone who seemed so vivacious and kind to others could have wanted to end his own life.

Although he has denied ever being diagnosed with any mental illness, Williams admitted he struggled several times with addiction and periods of “feeling sad.” But one mental health counsellor says the kind of depression Williams must have been dealing with must have been “so much more than simply 'dealing with demons'."

“This is an illness that is all too pervasive that is now finally being forced into the spotlight,” Mark Henick, a mental health counsellor with the Canadian Mental Health Association in Toronto told CTV News Channel on Tuesday.

The fact that Williams was, by most measures, a “success” in his career, as well as beloved by his peers and his fans is irrelevant to any mental health issues he may have had, Henick says. Because anyone, no matter how successful they are, can succumb to depression.

“Mental illness or addiction know no boundaries. You can be rich or poor, black or white, any race or religion,” he said.

People suffering from severe depression become overly focused on their failures, not their successes. They have a hard time ignoring their own negative thoughts until they reach a point where they no longer can control their thoughts.

“These kinds of struggles have a way of restricting their perception in a way that they really can't see any other options. This is how they cope. They've learned maladaptive coping mechanisms over decades of their life. And it can be really difficult to break that cycle without some really meaningful help,” Henick said.

Andy Nulman, the co-founder of the Just For Laughs comedy festival who met Williams several times, works with AMI-Quebec (Action on Mental Illness) and points out that one in five people will suffer from mental illness at some point in their lives.

“I know that this is prevalent. Someone asked me yesterday if this is prevalent in the entertainment industry and I said, 'Of course it is. But it's prevalent in any industry',” he told CTV’s Canada AM.

Henick says the vast majority of people who die by suicide -- over 90 per cent -- have a diagnosable mental illness at the time of their death. Sometimes there are triggers, such as major life changes or the death of loved one, that can set someone on the path to depression. Other times, it’s not clear what sparks it.

Treatment typically includes psychotherapy, to help break the negative thought cycles, and sometimes anti-depressive medication.

It’s not yet known if Williams was receiving any help for his depression. He entered alcohol rehab in July -- for a checkup, his manager said at the time -- and his publicist quickly released a statement after the actor’s death to say Williams had been suffering from severe depression. Both suggest that those who loved the comedian knew he had been struggling in recent weeks and had attempted to get him help.

Williams had been successfully treated in the past for drug abuse and alcohol abuse. Henick says perhaps this time, the help came too late.

“Or, he may have been struggling too much.”

According to the Diagnostic and Statistical Manual of Mental Disorders, the so-called "psychiatric bible", clinical depression or "major depressive episode" is defined as a period of two weeks or longer with the presence of 5 or more of these symptoms:

  1. Depressed mood most of the day.
  2. Diminished interest or pleasure in all or most activities.
  3. Significant unintentional weight loss or gain.
  4. Insomnia or sleeping too much.
  5. Agitation or psychomotor retardation noticed by others.
  6. Fatigue or loss of energy.
  7. Feelings of worthlessness or excessive guilt.
  8. Diminished ability to think or concentrate, or indecisiveness.
  9. Recurrent thoughts of death