Dream Alien
The "Dream Aliens" were a corporeal telepathic humanoid species, who lived out their lives in a dream state. Native to an unidentified planet in the Delta Quadrant, they (or at least a group of them) existed in a cavern, so as to not be easily found. ()

History 
The representative Dream Alien encountered by Chakotay claimed that for centuries, what they termed the "waking species" had come and found them in their so-called sleep state and tried to destroy them. 

By the 2370s, they had found a way of defending themselves against the "waking world", which involved a machine that broadcast a neurogenic field over the distance of several light years. With this, they could invade the dreams of nearby starships, and eventually force their crews to go to sleep. 

While this dream state appeared to be simple sleep based on analysis by The Doctor, he was incapable of waking any of the affected victims up using artificial means such as drugs or external stimulants, although he was able to provide drugs to keep the crew awake so they wouldn't be trapped in the dream. After the crews fell asleep, they would all be trapped in a shared dream, theorized to be a collective unconsciousness, in which the aliens would take over the ship.

 was attacked in this way in 2374, but they were defeated by Commander Chakotay, who had unusual command of his dream using a technique called lucid dreaming, allowing him to plant a "trigger" in his mind where his subconscious would include Earth's moon in his dream, allowing him to realize that he was dreaming and wake himself up. With this method – and the aid of The Doctor, who, as a hologram, never slept – Chakotay was able to stay awake long enough to locate the sleeping aliens in a cavern on their homeworld by tracking the energy field they created to maintain their enemies' dream state. 

Unable to deactivate the field generator with his phaser, as it was protected by a forcefield, Chakotay opted to wake one of the Dream Aliens instead. With The Doctor ordered to launch a photon torpedo at the cavern if Chakotay didn't respond within five minutes, Chakotay once again fell asleep and confronted the aliens with a final ultimatum, forcing them to dismantle the transmitter that the aliens used for their dream attacks and end the crew's nightmares before The Doctor destroyed their physical bodies. 

As of their discovery by Voyager in 2374, this species had never been assimilated by the Borg. ()

Biology

Anatomy 

They were physically described by Kathryn Janeway as having "sharp ridges on [the] forehead and on the front of [the] neck." Tuvok generally agreed with Janeway's description, also describing the species as an "alien with ridges on [the] face and neck." To Chakotay felt he was a "vicious looking alien."

In reconstructing the appearance of the species for identification, it was indicated that their facial ridge height exceeded four centimeters, and the space between their eyes exceeded three centimeters. They also had a small distinctive horn spouted from their chin. Their skin color and texture were notable orange.

Upon encountering them in the waking world, Chakotay noted that their corporeal bodies looked "pretty frail". ()

Physiology 
This species existed in a collective unconsciousness, which they considered to be their reality. As having never had encountered beings of this nature before, following first contact, Chakotay wondered aloud "how did they evolve this way" and if "they ever [woke] up"?

Upon noting their apparent frailty, Chakotay theorized that "they probably wouldn't have the same tolerance for stimulants that we do." Keeping that in mind, he proved his theory after giving one of the Dream Aliens a dose of animazine. ()

Technology 
See
 Dream Alien ship
 Harmonic inversion technology

Individuals 
 Unnamed Dream Aliens

de:Traumspezies
Unnamed species
Telepathic species
Memory Alpha articles named from scripts‎