The deaths of a number of celebrities may well be warnings about the dangers of chronic sleeplessness.

When a star dies from an overdose, there's a tendency to write it off as "drug abuse." That amazing combination of drugs in Heath Ledger's body, for instance -- what was he thinking? Blame the celebrity, chalk it up to reckless living, a self-destructive lifestyle, a pursuit of pleasure through recreational drugs.

But the drugs that killed Ledger -- three types of benzodiazepines, an antihistamine, two pain relievers -- are all substances people take for sleep. Ledger, we know, was desperate for sleep. A month or so before his death, he told the New York Times that he was going night after night on no more than two hours of sleep.

He was described by his ex, Michelle Williams, as having a mind "turning, turning, turning." That might explain the variety of benzodiazepines he took that night -- Valium, Zanax and Restoril. All are effective at quieting a whirring mind.

Imagine what it would be like being a celebrity with a sleep disorder: the early morning shoots, the need to look bright-eyed and beautiful before a camera, the world watching, at close range, as you get hollowed out and haggard from lack of sleep. You'd need nerves of steel to live in the public eye like this; you'd need a "head-hits-the-pillow-and-I'm-out" kind of sleep system -- which not everybody has. Some stars, such as Eminem and Drew Barrymore, speak openly about their insomnia; I'm sure there are many more who do not.

I wonder how many stars have died just because they were trying to get some sleep. Elvis Presley had serious insomnia, by his ex-wife's account, and ultimately became addicted to Placidyl, a sedative so dangerous that it's no longer on the market. He would have had to increase the dose to keep getting the same effect, as one does with most sleep medications, even the newer ones -- but those older drugs are longer acting and build up in the system over time, leaving users dopey, groggy, in a permanent fog. Elvis then turned to Dexedrine to wake himself up, according to his ex-wife, and got caught in a vicious cycle. Official cause of death: heart failure.

Judy Garland also got hooked into that cycle: uppers to control her weight, sleeping pills so she could sleep; she too would have had to increase the dose to get an effect. Official cause of death? Accidental overdose from a barbiturate, Seconal.

Marilyn Monroe's death was ruled a "probable suicide" by the L.A. County coroner's office but is thought by many to have been accidental, possibly because of a miscommunication between her doctor and psychiatrist, one giving her Nembutal, a barbiturate, and the other giving her chloral hydrate, the medication most prescribed for sleep before there were barbiturates. There are many theories about her death, of course, but one likely scenario is that she was just trying to get to sleep.

Anna Nicole Smith? Chloral hydrate, again. She told friends she'd built up a tolerance to it; she would have needed more to get the same effect. She was obviously mixing it with other medications -- there were four benzodiazepines in her bloodstream: Valium, Serax, Ativan and Klonopin, in addition to an antihistamine and a GABA agonist -- all of which can be taken for sleep.

Who knows what goes through a person's mind when they reach for that final, fatal dram? "She had long since raised the dose to its highest limit, but tonight she felt she must increase it," writes Edith Wharton about her character, Lily Bart, at the end of The House of Mirth, as Lily squeezes out the extra drops of laudanum that put her into a sleep from which she never awakens. "The action of the drug was incalculable, and the addition of a few drops would probably do no more than procure for her the rest she so desperately needed."

In my research on insomnia, I have spoken to quite a few people who told me that they had reached a point at which they just didn't care, they'd do anything to sleep: "At least if I died, I'd get some rest," one insomniac said. The celebrated Swedish physician Axel Munthe, who had more success treating the insomnia of his patients than he did his own, wrote in his 1929 bestseller, The Story of San Michele: "Insomnia does not kill its man unless he kills himself -- sleeplessness is the most common cause of suicide. But it kills his joie de vivre, it saps his strength, it sucks the blood from his brain and from his heart like a vampire."

We've been taught to see insomnia as secondary to, as resulting from, depression, neurosis or other sorts of psychopathology. But there is increasing evidence that it may work the other way around: Insomnia may be the cause and not the consequence of a person's emotional instability. Insomnia is now known to be a risk factor for depression, alcoholism and suicide.

And research suggests that how well or badly we sleep may have as much to do with genetics, with a physiological predisposition to fragile sleep, as with anything we're doing to mess ourselves up. Studies of twins by Andrew Heath of the department of psychiatry at Washington University in St. Louis, and by Belgian researcher Paul Linkowski have found that identical twins, even when not raised together, have sleep patterns more similar to one another than do nonidentical twins or other sibling pairs, in terms of bedtime, length of sleep and quality of sleep.

Studies of the molecular mechanisms of normal sleep and sleep disturbances by University of Zurich researcher Hans-Peter Landolt, Stanford University researcher Emmanuel Mignot and Washington University researcher Paul Shaw, among others, also suggest that differences in sleep behavior are genetically determined.

Insomnia may soon be on a growing list of conditions, including ulcers and migraines, that were once attributed to neurosis but are now known to have neurobiological bases. Several sleep disorders -- narcolepsy, restless legs syndrome, REM behavior disorder -- have already been added to the list.

To be sure, many stars live wildly, recklessly. They rocket to dazzling heights, then fall precipitously, leaving onlookers amazed at the spectacle. Maybe it satisfies our sense of drama to see their ends as somehow fitting -- spectacular endings to spectacular lives, poetic justice, the price of fame. But probably some of them were just trying to get to sleep.

Surveys suggest that as much as 10% to 15% of the U.S. adult population suffers chronic insomnia -- that is, continuously, enough to drive them to incautious use of medications. Many of these people are functionally disabled, unable to get or hold a job; some are so debilitated that they're constantly ill, at the mercy of every passing bug. Insomniacs have statistically more visits to the doctor, more hospitalization, more accidents on the job and on the road. It's impossible to function when you're getting less sleep than you need over a long period of time.

But the stigma attached to this disorder -- that it's neurosis or psychopathology or a condition we bring on ourselves -- makes many of us choose to quietly increase our dosage rather than reach out to seek help. Why wasn't there an insomniacs' hotline Ledger could call? Why haven't insomniacs organized? People with rarer sleep disorders, like narcolepsy and restless legs syndrome, have founded advocacy groups that are drawing attention and funding to these conditions.

But insomniacs have not. And so insomnia remains an under-researched and little understood condition, more likely to be seen as the fault of the victim than given the kind of treatment that helps.

A coroner's report concluded that Ledger's death was an "accident" -- "the result of acute intoxication by the combined effects" of the drugs he took that night, drugs he almost certainly took for sleep. Maybe we should revisit that old saying, "nobody ever died of insomnia." Ledger helped break the silence on this issue. Let's keep talking.

Gayle Greene, a professor of literature and women's studies at Scripps College, Claremont, is the author of "Insomniac," a first-person account of living with insomnia and an investigation of what is known about the disorder.