The Region of Dreams is composed of the dreamscapes, which is an ever changing section of the plane where anything is possible, and the Dreamheart, a region of wildly shifting energies where abandoned dreams break down. The Dreamhart is very dangerous, as the dream fragments can form a dangerous mealstrom, and death within its boundries is permanent, with no hope of having ones soul travel to an outer plane.
At the edge of Dreamheart is a portal leading to a demiplane known as the Plane of Nightmares.
The Plane of Nightmares is much like the Region of Dreams, except that all dreams here shift toward insanity and fear. Originally, this plane was part of the Region of Dreams, but long ago, an ancient group of wizards sought out power by tapping into realms accessible only through their dreams. Eventually, this search for power allowed the dreaming wizards to contact the Far Realm, and drew its power through the Region of Dreams. This caused many problems within the Region of Dreams, and the influence of the Far Realm made twisted nightmares real, and eventually, the Region of Dreams was divided by the Nightmare Gate, and the Plane of Nightmares was separated from the Region of Dreams.