So you fell asleep easily enough, but now it’s 3 a.m. Your mind is spinning, and rest is elusive. You’re reliving every foolish or embarrassing thing you did in the past 24 — or 48 or 72 — hours, and that is a lot of material to run through. And you simply can’t stop.

Except maybe you could, if only you knew how to be mindful.

“When you’re caught in that loop of rumination, that’s very real, and it creates very intense feelings,” explains psychologist and journalist Daniel Goleman, who reported on brain and behavioral sciences for the New York Times. “If you’re mindful, you realize it’s just a thought. You don’t have to believe your thoughts. You can question them, and that changes them. It takes energy from the brain that creates the heaviness. Looking at it in a different way makes the rumination less intense.”

You might think, on hearing such praises of mindfulness — a form of meditative practice — that it will solve just about every problem in your life. Meditation can halt the late-night rumination cycle, right? So can’t it also make you into a better person? Enlarge your brain? Make you taller and thinner and richer?

Well, no, says Goleman, who’s also the author of the best-selling book “Emotional Intelligence.” Some claims of meditation’s power are overblown. Some studies are less rigorous than they should be. But science has proven that meditation can induce healthy and important physical improvements, such as lowering your blood pressure, decreasing relapses into depression and managing chronic pain.

Which leaves us with a question: As our interest in meditation grows, how do we know what’s too good to be true?

Goleman has some answers. With Richard J. Davidson, who directs a brain lab and founded the Center for Healthy Minds at the University of Wisconsin-Madison, Goleman has just published “Altered Traits: Science Reveals How Meditation Changes Your Mind, Brain, and Body” (Avery, $27). The book separates truth from fiction, debunking studies and highlighting truth about meditation’s startling effects on the brain.

“Altered Traits” also chronicles the authors’ decades-long friendship and lifelong interest in the subject of meditation, which began at a time during which scientific circles had little patience or interest in the subject.

The book is important because it represents “the coming together of two very important voices,” says Scott Rogers, founder and director of the Mindfulness and Law Program at the University of Miami School of Law.

Rogers, co-founder of UMindfulness, the university’s inter-disciplinary collaboration that marries research to training, notes another benefit: Not only are Goleman and Davidson experts in their fields, they’re also meditation practitioners.

“We need responsible, reasoned voices speaking from a variety of perspectives, and here we have the hard science and the journalist, and both are practitioners. We need a book we can look to as a reliable source of information,” Rogers says. “They both practice and have for a long time. A lot of researchers have been interested in this over the last 10 or 15 years, but they haven’t historically practiced mindfulness. There are a bunch of people practicing, but they’re not scientists.”

“Altered Traits” examines scientific studies on meditation and the benefits of intensive retreats, learning to view our selves and our brains in a whole new light and the importance of a good teacher (“I feel strongly the quality of the teacher is important,” Goleman says). The book also challenges notions we (or at least our bosses) hold dear, such as the idea that multitasking is a positive endeavor.

“Multitasking is a myth,” Goleman says. “You can’t really do two things at once. What happens is your brain switches rapidly. As it switches, you lose the power of your concentration. You do many things at once, you do them less well.”

But there is good news for multitaskers, according to “Altered Traits”: Cognitive control can be improved. One test of undergrad volunteers tried short sessions of focusing or breath-counting. “Just three 10-minute sessions of breath counting was enough to appreciably increase their attention skills on a battery of tests. And the biggest gains were among the heavy multitaskers, who did more poorly on those tests initially,” the authors write.

Which brings up another important question: If the benefits of meditation expand the deeper a person’s practice goes, is meditating in short sessions still useful?

Goleman says yes.

“Casual practice helps you in surprising ways, but the deeper you go and the more you practice, the more benefits you get,” he says. “The research shows that right from the beginning mindfulness practices counter the ill effects of multitasking. We’re all doing so many things a day. But the improvement in attention starts at the beginning.”

And if you can only spare 10 minutes at a time for meditation, Goleman suggests spreading your practice throughout the day.

“Intersperse it through the day. Ten minutes in the morning. Ten at lunch. Ten at night. The effect is prolonged. If you can do 20 minutes, even better. If you can do it for a year, that’s good. Five years is even better.”