On Monday afternoon, while watching the first TV news reports of Robin Williams’s suicide, I found myself laughing. And here I should probably note that the laughter was not of the knee-slapping variety. Nor was it gallows laughter of the sort Williams himself had always embraced and evoked. Mine was a distinctly nervous laughter—low, fast, guttural—emitted through gritted teeth; it was the sound a cornered dog makes when he doesn’t know whether to fight or flee.

Anyone with half a soul had to be at least a little shocked to learn that one of America’s most beloved funnymen had hung himself. But the bad news tends to be doubly troubling to those of us who, like Williams, have suffered from depression—an affliction that has bedeviled an estimated one in 10 American adults, according to the C.D.C., including me. To see someone like Williams take his own life is to instinctively fear for one’s own future.

Despite my personal history, my upset was hardly unique. I know this because CNN kept telling me so—although possibly it was MSNBC, or HLN, or whatever. After a while, I was flipping channels so frequently that the various anchors morphed into one giant haircut barking questions at Dr. Drew. And the ubiquitous multi-media personality, who is basically the Ryan Seacrest of doctors, calmly explained, “It’s almost unimaginable how someone who has so much joy in his life, and who brings so much joy to others, could be in a state of misery.”

Not to me, it wasn’t.

I never met Williams, and I was never among his biggest fans. Although my teen years directly coincided with Mork-mania, all that zaniness and shouting eventually left me cold and exhausted. And no matter how much I liked him in The World According to Garp, Good Will Hunting, and One Hour Photo, I could never forget the twee trifecta of Patch Adams, Jumanji, and Jakob the Liar.

For the past several years, though, Williams increasingly occupied a small corner of my psyche. He first arrived there in 2000, while I was reporting a Vanity Fair article about Jay Moloney, a young Hollywood talent agent who had committed suicide in late 1999. Moloney had reportedly been, in addition to a cocaine addict, a manic-depressive.

Back then, I was among the large majority of people who knew nothing about manic-depression—a vicious and fairly pervasive mood disorder that few people seemed comfortable talking about. It would take upwards of a decade before bipolar celebrities—Catherine Zeta-Jones, Russell Brand, Patrick Kennedy—would start stepping forward. When I consulted an expert on the subject, she explained that “manic-depression” is really just another term for bipolar disorder, and that the condition is marked by perilous mood swings—from deep depression to high-wire mania.

Depression I understood (although not really). But mania I had trouble grasping. It seemed so vague. “On the one extreme, mania can reach the point of full-on delusion and madness,” the expert said. “On the milder side, it’s basically a very hyper person—euphoric, grandiose, bursting with ideas.” She paused. “Just picture Robin Williams.”

The image stuck. Because it was perfect.

Since then, I’ve seen a little Robin Williams in every manic-depressive I’ve since come across in my research and reporting. And I’ve come across several of them while reporting for V.F. The first was Bruno Zehnder, an eccentric penguin photographer, who froze to death in 1997. Then came Timothy Treadwell, the hyperkinetic bear enthusiast better known as “The Grizzly Man.” Both men were nothing if not potential real-life Robin Williams characters: half-mad charismatics who burned brightly. And, like Williams, they died lonely, violent deaths.

For the record: I can’t say whether or not Williams was bipolar. Some media reports suggest he was; others say he wasn’t; others play it vague. In 2006, Williams told NPR’s Terry Gross that he never been diagnosed with either manic-depression or clinical depression. Today, with the benefit of hindsight, it’s easy to divine some artful hedging in his explanation: “Do I perform sometimes in a manic style? Yes. Am I manic all the time? No. Do I get sad? Oh, yeah. Does it hit me hard? Oh, yeah.”

So maybe he was. Maybe he wasn’t. Or maybe, like many people with psychiatric issues, he simply defied categorization. Bipolar disorder isn’t something doctors can identify through X-rays or blood tests; it’s part of a broad diagnostic spectrum that’s open to interpretation. Manic-depressives can be misdiagnosed as depressives, and vice versa. I was once diagnosed as bipolar; later, I was un-diagnosed.

Point being: to me, and to many people like me, it doesn’t really matter whether or not Williams was officially bipolar. What matters is that his behavior represented manic-depression. He was its platonic ideal, the happiest personification of itself. This I learned years ago, while recovering from my first and only manic episode. (Hence the diagnostic revisionism.) I was sitting in the psych ward’s main TV room when I realized that half the manic-depressives in residence—or, rather, half the manics—sounded exactly like Williams. The exuberant stories they told (and told) were decidedly non-linear.

From this point forward, I followed the ups and downs of Williams’s life with equal measures of warmth and fear. The latter stemmed from a certain foreboding I felt during his newer on-screen appearances. His comedy had always betrayed degrees of melancholy and madness. But by last fall, when he starred in a doomed sitcom CBS sitcom called The Crazy Ones, his eyes seemed sunken. His comic riffs were downright manic. And when I heard he’d been in poor health, I remember thinking: Uh-oh.

Which brings me back to why I found myself laughing in the face of a truly awful death. I partly attribute the laughter to sheer incredulity. I just couldn’t believe this was happening again, to yet another sparkly manic-depressive (or whatever he was).

Admittedly, though, there was something mirthful in my laughter. But there’s an explanation for that. For some reason, the tragic news took me back to a memory of a hallelujah moment I’d experienced during my brief period of madness. One day, mid-story, one of the manics was brusquely interrupted by a “straight” depressive patient. “You sound like fuckin’ Mork from Ork,” the straight complained. To which the manic replied, with a Williams-ian flourish, “Thank you!”

Ned Zeman is the author of "The Rules of the Tunnel: My Brief Period of Madness."