Nightmare's realm is not part of The Mindscape, but the Sleepwalkers are aware of him and consider him an enemy. Because Sleepwalkers do not have to sleep, Nightmare has never been able to affect or dominate them. He sought to do this through the hero Sleepwalker, who had been connected into the brain of the human Rick Sheridan. Nightmare sent Sleepwalker back to his own realm, with a monitor to assure the hero Rick was not being tormented. Rick was being tormented, with the intent of driving Sleepwalker mad and thus giving Nightmare access to the minds of Sleepwalker's people. The hero was not fooled and sacrificed his return home in order to stop Nightmare.