(CNN) The most important hour of "The History of Comedy" -- an eight-part CNN documentary devoted to stand-up -- might be the most serious and sobering: the high toll comedy exacts on its practitioners, from depression to substance abuse.

The tears of a clown almost sounds like a cliché, but given the high-profile examples of comics who died young or took their own lives -- among them John Belushi, Chris Farley, Robin Williams and Richard Jeni -- it's more than just a song title. And in that upcoming segment of the program, subtitled "Spark of Madness," comics talk with considerable openness and honesty about the exaggerated highs and lows associated with their work.

"A lot of comedians are people that are very introverted, very shy, very sensitive to humiliation," says Patton Oswalt, adding that it's common for them to be "a little narcissistic, a little damaged."

As Gilbert Gottfried notes, it's not unusual for people to lament after a tragedy, like Williams' suicide in 2014, how someone could be so buoyant and talented and yet so plagued by demons and excesses. The two, he suggests, are intertwined, much like the masks of comedy and tragedy.

What "History of Comedy" does within that hour is to bring what are often viewed as isolated incidents into context. Programmed to probe for universal truths and bare their souls on stage, the comics interviewed also prove extremely open and honest in discussing these issues, including how drugs often serve as a means of replicating the high that they get from performing.

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