Nagai Yume (長い夢; lit. "Long Dream") is a short story by manga author Junji Ito, originally included in The Junji Ito Horror Comic Collection. A one-hour Japanese television drama adaptation was broadcast in 2000. The adaptation was directed by Higuchinsky, whose film adaptation of Ito's Uzumaki had been released earlier the same year. The story was also adapted in the second segment of the second episode of the anime Junji Ito Collection.

Dr. Kuroda, a celebrated neurosurgeon, expresses severe doubt when a patient named Tetsuro Mukoda is admitted, complaining of increasingly long dreams, although his assistant, Dr. Yamauchi, believes there may be some truth to Mukoda's complaints. Another patient at the hospital, Mami Takeshima, who was admitted for treatment for a benign tumor, begins experiencing a heightened fear of death and has a harrowing encounter with Mukoda, who wanders the halls at night, too afraid to sleep.

Though he continues to believe Mukoda's symptoms are just hallucinations, Dr. Kuroda agrees to admit him and decides to study his symptoms in detail. Using an EEG machine, Kuroda discovers that when Mukoda sleeps, there are brief periods when he enters rapid eye movement sleep, spanning just a few seconds at a time. During this period, his brainwaves become erratic and his eyes thrash about wildly, only to suddenly stop. In that brief moment of REM, he is in the depths of his condition.

With each passing night, the perceived length of Mukoda's dreams seems to be increasing, from months to years to decades, and then to centuries, and often the experiences he suffers while dreaming are extremely unpleasant. As his dreams continue to lengthen, Mukoda begins to experience amnesia when he wakes up, often having to be reminded by Kuroda as to why he was admitted to the hospital. His mannerisms and intonation also begin changing, as if he was speaking as a person from a different century. Mukoda becomes pale and gaunt over time as his illness worsens. Mukoda continues to suffer from his long dreams, and eventually undergoes extreme physical mutations as his dreams become several millennia long within his mind; it is as if Mukoda is living the length of time he perceives his dreams are, somehow experiencing evolution while still alive.

The psychological effects of his condition have also only continued to worsen, to the point that he can no longer differentiate his dreams from reality. Believing that Takeshima is his wife from within the dream world, a severely mutated Mukoda accuses Kuroda of trying to interfere in their 'relationship' upon waking and accosts Takeshima. Shoving the doctor aside, Mukoda runs to Mami's room with Kuroda in hot pursuit. Terrified, Mami accuses Mukoda of being death, before Kuroda manages to intervene. Mukoda comes to his senses and asks, "What happens to the man who awakens from an eternal dream?"

Mukoda's mutations continue to worsen, and eventually, he barely resembles a human at all. One night, while Kuroda continues to study him, Mukoda enters REM sleep again and finally experiences an eternal dream. Kuroda, who had himself fallen asleep due to fatigue, awakens to see the result; with his spirit fleeing his body, Mukoda crumbles away into dust, leaving behind strange red crystals.

Shortly afterward, Takeshima confides to Yamauchi that her fear of death is lessening but that she, too, is starting to experience long dreams. Theorizing that the illness Mukoda suffered from is contagious, Yamauchi consults Kuroda on the matter, who explains that he had been using the crystals on Takeshima in secret, having realized they were the secret to Mukoda's condition. Yamauchi is horrified by this, stating that it desecrates the souls of the dying, but Kuroda reasons that humanity will have no reason to fear death if they have the option of having eternal dreams instead.

In the television drama, the conclusion of the story continues beyond Mukoda's demise, and is significantly different from the ending of the story on which it is based.