A new national study that claims almost half of Americans will be mentally ill at some point in their lives made me laugh out loud. This had to be a joke, or at least a gross overstatement, I figured. And if it happens to be true, well then, Americans are a lot crazier than I thought.

But then I started running down the list of mental disorders provided by the National Institute of Mental Health, the main supporter of the study – and found quite a few that apply to me.

My fear of heights, which is a phobia. The attacks of agoraphobia (fear of wide-open spaces) that I suffered years ago while traveling out west. The bouts of generalized anxiety that have kept me from sleeping. The separation anxiety/panic attack that once kept me from closing on a real-estate purchase and resulted in my losing a huge deposit. And the extended bouts of depression that are now, thankfully, in the past.

I also thought about the mental disorders that have dogged people I know. The friend who experiences chronic depression, feelings of worthlessness and suicidal thoughts. The ex-husband who had an impulse control disorder that made him intermittently violent. Several former colleagues who found fault with every work situation they were in – “oppositional-defiant disorder” perhaps – and could never hold onto any job for long. And several people I know whose lives have been ruined by drug dependency.

The light side of this story is that we’re not alone in our occasional nuttiness. But the dark side is that a lot of minor mental disorders start in childhood and, if left unrecognized and untreated, can develop into serious mental illness that can dramatically pull down people’s lives.

I’m thinking about the 9-year-old Brooklyn girl who stabbed her 11-year-old friend to death earlier this month. Her behavior seemed like a bizarre fluke at the time, until reports started coming in about how she had engaged in a number of violent episodes previously. Perhaps if her obvious problem with impulse control had been diagnosed and treated earlier, this tragic murder could have been avoided.

For others, mental disorders fester and explode in adulthood. And while not every phobia, anxiety or behavioral problem turns into serious mental illness, there are plenty of people for whom life is an unnecessarily hard struggle because their disorders are never recognized or treated.

Why? Because it takes them a long time to figure out that something’s wrong, and when they do, they don’t know what it is or what to do about it, says Dr. Kathleen Merikangas, a senior investigator at the National Institute of Mental Health and a co-investigator on the study. Sometimes, even when they try to get help, the response is inadequate or incompetent.

Many New Yorkers are as likely to have a psychotherapist as they are to have a physical fitness trainer. But it’s still a middle- and upper-middle-class thing. I think of all the working-class folks in this city who probably need therapy but don’t know how to get it, and of all the people outside the big cities, where therapy isn’t considered as cool.

There’s also the matter of health insurance. A 1999 survey by the federal Substance Abuse and Mental Health Services Administration found that an estimated 3.2 million Americans suffering either from depression, general anxiety or panic attacks were medically uninsured.

In view of the study results, I can envision a national public service campaign to make Americans more aware of mental disorders, and how they can get help for them – just like the campaigns we’ve done about teenage pregnancy, drug abuse, AIDS and domestic violence.

To me, the main message of this study is that a lot more people than we imagined are mentally sick, and there’s no reason they should be suffering needlessly.