This slightly preening sense of specialness is not uncommon among insomniacs—particularly, it seems, the writerly sort. Bertrand Russell observed that “men who are unhappy, like men who sleep badly, are always proud of the fact.” Such pride, he speculated, was a feint on their part—an effort to turn a frailty into an advantage—and perhaps he was right. Vladimir Nabokov’s famous dismissal of “the moronic fraternity” of sleep certainly sounds like someone turning up his nose at a club that won’t have him: “I simply cannot get used to the nightly betrayal of reason, humanity, genius. No matter how great my weariness, the wrench of parting with consciousness is unspeakably repulsive.” But in the insomniac’s self-satisfaction there is also, perhaps, a genuine fear of the nonbeing, the nullity, of sleep. When Benjamin discusses her dislike of mindfulness and meditation techniques, she remarks that she is terrified of the “stupefaction” and “blankness” to which she imagines they lead. She yearns for the replenishment of sleep, but she doesn’t want “to slip unknowingly from being into nothing.” Aristotle called sleep “a privation of waking,” and a simultaneous longing for and resistance to that privation seems to lie at the heart of insomnia’s torment.

Alice Robb’s book “Why We Dream” (Houghton Mifflin Harcourt) is a spirited rebuke to the idea of sleep as a mere parting with consciousness. In exploring the pleasures and uses of dreams, she seeks to persuade us that sleep is not just the “off” to waking’s “on” but another realm of being, a second consciousness, rich in adventure and wisdom. The contemporary indifference to our dream lives, she writes, is a regrettable historical anomaly, one that leads us to squander “five or six years’ worth of opportunity (20-25 percent of total time asleep) over the course of an average lifetime.”

The greater community of dream enthusiasts includes, by Robb’s own admission, a fair number of cranks. At the annual conference of the International Association for the Study of Dreams, held in a medieval abbey in the Netherlands, she encounters people who believe in dream telepathy, and in using “energy fields” for dream interpretation. She also attends a dire-sounding Dream Ball, at which attendees dress up as characters and enact scenes from their dreams. Nonetheless, she is able to tread a careful and persuasive line between robust skepticism and open-mindedness, resisting the tendency of some dream explorers to conflate “their own intuition with evidence,” but also acknowledging that the line between mystic garbage and truth can be blurry. She quotes a Harvard psychology professor, Deirdre Barrett, who accepted a paper on extrasensory perception for the academic journal Dreaming, which she edits. “My stance is that what defines scholarly research is the approach and the design,” Barrett says. “It’s anti-science to insist on a conclusion.”

Science has long understood that REM sleep—the stages of sleep characterized by rapid eye movement, in which most dreaming takes place—plays a vital role in our mental health. The human need for REM is so uncompromising that, when it is inhibited over a long period by excessive alcohol use, the pent-up backlog will release itself in a form of waking psychosis, otherwise known as delirium tremens. For a long time, the scientific establishment suspected that dreams were a superfluous by-product of the REM state. But in recent decades, thanks in large part to the advent of brain-imaging machines, scientists have been able to establish that dreams themselves are essential to the benefits of REM sleep. First, dreams knit up the ravelled sleeve of care by allowing us to process unhappy or traumatic experiences. Typically, during the REM state, the flow of an anxiety-triggering brain chemical called noradrenaline is shut off, so that we are able to revisit distressing real-life events in a neurochemically calm environment. As a result, the intensity of emotion that we feel about these events in our waking lives is reduced to manageable levels. In “Why We Sleep,” Walker attributes the recurring nightmares of P.T.S.D. sufferers to the fact that their brains produce an abnormal amount of noradrenaline, preventing their dreams from having the normal curative effect. When the dreaming brain fails to diminish the emotion attached to a traumatic memory, it will keep trying to do so, by revisiting that memory night after night.

Dreams also help us to master new skills; practicing a task or a language in our sleep can be as helpful as doing so when we are awake. And they appear to be crucial in honing our capacity for decoding facial expression: the dream-starved tend to slip into default paranoia, interpreting the friendliest expressions as menacing. Perhaps most alluring, dreams help us to synthesize new pieces of information with preëxisting knowledge, and to make creative lateral connections. The long list of inventions and great works said to have been generated in dreams includes the periodic table, the sewing machine, Coleridge’s “Kubla Khan,” Paul McCartney’s “Let It Be,” and Mary Shelley’s “Frankenstein.”

According to Robb, there is a means by which we can harness the visionary and problem-solving capacities of dreaming: the lucid dream. This is the kind of dream in which a person is aware of dreaming, and is able to wield some control over events—to decide to fly, say, or to visit Paris. “Those who master lucidity,” Robb writes, “can dream about specific problems, seek answers or insights, stage cathartic encounters, and probe the recesses of the unconscious.” Fifty-five per cent of people have experienced lucidity at least once, apparently, but most of us need to train ourselves to dream lucidly with any consistency. The main training method requires you to ask yourself at regular intervals during the daytime whether you are asleep or awake. The idea is that, since waking habits have a tendency to show up in dreams, you are likely to pose the same question while you are asleep. When you ask yourself “Am I awake?” and the answer is no, lucidity should theoretically commence.

Oscar Wilde is said to have identified the most frightening sentence in the English language as “I had a very interesting dream last night.” Robb, who regularly attends dream groups at which people take turns analyzing one another’s dreams, fiercely disputes this prejudice. “One of the saddest consequences of our cultural contempt for dreaming is the trope that dreams make for boring conversation,” she writes. Whether she helps or hinders her argument by citing the dream-centric badinage of the Rarámuri tribe of northwestern Mexico is debatable. The Rarámuri, for whom “ ‘What did you dream last night?’ is rivalled only by ‘How many times did you have sex?’ as the most popular morning greeting among men” will strike many readers as an excellent advertisement for the virtues of discretion on oneiric matters.

The two chief factors determining your interest in someone else’s dreams would seem to be your level of emotional investment in the person telling the dream and the extent to which you believe that dreams can be intelligently interpreted. Nabokov, who had quite a rich dream life and often used dreams in his fiction, was briefly taken by a hokey theory that dreams were precognitive, but otherwise he maintained that they were without significance, a stance probably influenced by his extreme antipathy to Freudian theory. “I have ransacked my oldest dreams for keys and clues,” he wrote, “and let me say at once that I reject completely the vulgar, shabby, fundamentally medieval world of Freud, with its crankish quest for sexual symbols (something like searching for Baconian acrostics in Shakespeare’s works) and its bitter little embryos spying, from their natural nooks, upon the love life of their parents.” By now, widespread disenchantment with Freud’s interpretive code has resulted in a wholesale dismissal of dreams’ latent content. In “Why We Sleep,” Walker concedes that dreams tell us something useful about our underlying emotional concerns, but he insists that the information they deliver is “transparent” and requires no interpretation. This is a convenient position for someone who is uncomfortable about the absence of any scientific method for validating interpretations, but it is not a very satisfactory one. What is the “transparent” meaning of the dream in which your teeth fall out? What is the unambiguous message of “Kubla Khan”?