Dream

A dream was a series of sensations in the mind during sleep. Dreams could allow revelations, communication and insights into the psychology of an individual. (TV: The Time Monster, Doomsday, PROSE: The Also People)

Like many aspects of the universe they had a guardian; the Crystal Guardian was the Guardian of Dreams. (PROSE: Divided Loyalties)

The Bodach fed on the energy produced by a mind when dreaming (TV: Dream-Eaters), as did the Nightmare Man. (TV: The Nightmare Man)

The Eleventh Doctor, Amy Pond and Rory Williams experienced two alternate dreams after being exposed to Psychic Pollen, both of which presented as reality. (TV: Amy's Choice)

Invasion via dreams
In 2010, the Nightmare Man invaded the dreams of Luke Smith, Clyde Langer and Rani Chandra, turning them into nightmares, and planned to do the same to the rest of the world. Luke had several nightmares in which his friends didn't care that he was leaving for Oxford University. Rani dreamed she was on the BBC News studio being convinced by Louise Marlowe to tell everything she knows about Sarah Jane Smith. Clyde dreamed he was working in a burger bar (instead of as an artist) and being taunted by an elderly Sarah Jane. The Nightmare Man was defeated when the three used their bond to overcome their fear and trapped him in the dream dimension, in which he was tormented by the elderly Sarah Jane, telling him how wonderful Luke was. (TV: The Nightmare Man)

In 2050, the Bodach caused all of London to fall asleep and dream. Starkey dreamed of chased by a Jixen in a strange place and running into Jorjie Turner and Darius Pike who sneaked behind an obelisk. He was terrified as he spotted a Bodach avatar moving behind them. When Starkey woke up he fled from a Jixen in his bedroom. When he found K9 Mark 2 he told him to shoot the Jixen. However, the alien threat K9 detected was Starkey and he terminated him. Starkey woke up after he was shot.

Darius Pike dreamed of being trapped in his car Mariah, surrounded by clowns who joined him in the car. In the waking world, when K9 discovered him shouting for help and to be let out, he observed Darius' behaviour as "strange" and remarked, "This one's going in the memory banks". Alistair Gryffen dreamed of the day he lost his family.

Jorjie went into June's nightmare in the Bodach's world with a fake love tattoo, distracting the furious June so Jorjie could pinch her, thus waking her up and freeing her from the Bodach's control. This allowed her to remove an Eye of Oblivion in the Bodach obelisk so K9 could destroy it. (TV: Dream-Eaters)

Visions of the future
On some occasions dreams were capable of foretelling the one's future, another's future or a possible future. Cassandra had dreams of the future, but no one took her warnings seriously. (TV: The Myth Makers)

In the 16th century Chris Cwej and Penelope Gate both had dreams of being in a room with no doors, this being a reflection of the Seventh Doctor's own concerns for his upcoming regeneration, and what he did to his previous incarnation. (PROSE: The Room With No Doors) In the 1970s on Earth, the Third Doctor dreamed of seizing power with the aid of a large crystal. (TV: The Time Monster)

While in the TARDIS travelling through the vortex, the Fourth Doctor was sent a Matrix projection of the assassination of the Lord President on Gallifrey. (TV: The Deadly Assassin) Also whilst in the vortex Leela had an apparently precognitive dream of the Fendahl. (TV: Image of the Fendahl) Ace also had dreams whilst in the TARDIS in the vortex of a woman in red and a door she couldn't open, a precognition of her encounter with the Chronovore known as Artemis that was locked within the Monk's TARDIS. (PROSE: Conundrum, No Future)

In 2009, Luke Smith had precognitive dreams about Mrs Wormwood. (TV: Enemy of the Bane)

A short time before Christmas 2009, everyone on Earth has dreams of the Master laughing, but everyone except for Wilfred Mott forgot about them after waking up. These bad dreams were also experienced by the Ood from the year 4226, but they knew more about the dreams. (TV: The End of Time)

Some dreams showed visions not of the future, but of alternate timelines that had been negated. Evelyn Smythe dreamed of her alternate self dying in the Tower of London, and the Sixth Doctor claimed that the memories of that timeline would live on in the dreams of the English people. (AUDIO: Jubilee)

Species of dreams
The Mara could manifest itself through dreams. On Deva Loka it was able to manifest itself in the dreams of Tegan Jovanka, using the personalities of Anicca, Anatta, and Dukkha. Following these manifestations the Mara was able to move from the dream world into the real world. (TV: Kinda) Tegan later had dreams of snakes (most likely a precursor to her second encounter with the Mara). (PROSE: Fear of the Dark)

Visitations in dreams
Visitations by individuals or communication through dreams on occasion occurred, although these visitations may have been an extension of the individuals' psychology. (see below)

The Black Guardian visited Turlough in a dream. (TV: Mawdryn Undead)

Death visited Ace in a dream. (PROSE: No Future)

Pain visited Benny in a dream. (PROSE: Set Piece)

While on Pete's World, Rose Tyler was contacted by the Tenth Doctor in a dream, which guided her to Dålig Ulv Stranden. (TV: Doomsday)

In his dreams, the Sixth Doctor was instructed by Voyager to return some star charts stolen by Astrolabus. (COMIC: Voyager)

Amy Pond was contacted by the Never-were in her dreams; they attempted to manipulate her into killing the queen of an unnamed insect race. (COMIC: Ghosts of the Never-were)

The Eleventh Doctor was visited by a hooded figure in his dreams, who told him that he was needed on Skaro. (TV: Asylum of the Daleks Prequel)

At one point, Vastra arrenged a conference call with Jenny Flint, Strax, Clara Oswald and River Song. Because Clara and River lived in different time zones, she arranged the call in a dream, saying that "time travel was always possible in dreams". In the call, Vastra told the Doctor's friends about how she found the space-time coordinates of the Doctor's greatest secret - Trenzalore. They awoke from the dream after they started being attacked by the Whisper men. (TV: The Name of the Doctor)

Dreams as an indication of psychology
Dreams were often an indication of the psychology of an individual: their fears, concerns, hopes, etc.

Barbara Wright, while a companion of the First Doctor, dreamed that she was back home with her mother, telling her that she was safe and having adventures throught time and space, and would one day return. The Doctor's TARDIS telepathically shared her dream with Joan Wright, who awoke reassured by it. (PROSE: A Long Night)

Zoe Heriot dreamed of her adventures with the Doctor after she was returned to her own time by the Time Lords, her subconscious mind having retained the memories they tried to erase. (PROSE: The Tip of the Mind)

Ace dreamed of being chased by a Dalek wearing a swastika and chanting, "Heil Doktor!" (PROSE: Timewyrm: Exodus)

Following her departure from the Spacefleet and return to travelling with the Doctor and Bernice, Ace dreamed of being naked and stabbing someone. (PROSE: Lucifer Rising)

Also following Ace's return from the Spacefleet and having seen the Doctor stand by as the Seven Planets were destroyed, Bernice Summerfield dreamed of Ace strangling her while the Doctor watched, saying, "It's for the good of the universe." (PROSE: Conundrum)

When facing the issue of what to do about Kadiatu presented to her by the Seventh Doctor, Benny dreamed of drinking and discussing evil and the nature of evil with a Dalek, a Cyberman, and a Sontaran. (PROSE: The Also People)

The Zygon Kritakh, while believing that he was in fact Michael Kirkwood, dreamed of being a Zygon. (HOMEVID: Zygon: When Being You Just Isn't Enough)

John Smith had dreams in which he was an adventurer in time and space called the Doctor, which he recorded in his journal. (TV: Human Nature)

The Doctor's dreams
The Doctor dreamed that the TARDIS was invaded by a servant of the Master of the Blackhole. (PROSE: Master of the Blackhole)

The Fifth Doctor dreamed that he was on a world being threatened by a burning comet. (PROSE: The Comet's Tail)

The Sixth Doctor dreamed that his adventures were broadcast on television. (PROSE: Christmas Special)

The Doctor had a dream about Sontarans in his TARDIS. (PROSE: Business Unusual)

The Seventh Doctor claimed to have once had a dream in which all his old enemies chased him around the sets of EastEnders. (PROSE: First Frontier)

The Eighth Doctor had a dream in which he had an adventure with his grandchildren John and Gillian. (COMIC: The Land of Happy Endings)

The Tenth Doctor dreamed of being chased by a Slitheen on a rocking horse. (PROSE: The Last Dodo)

The Eleventh Doctor was visited by a hooded figure in his dreams, who told him that he was needed on Skaro. (TV: Asylum of the Daleks Prequel)

Others' dreams
As a result of her genetics and in part related to the Pythia's curse, Kadiatu Lethbridge-Stewart dreamt of the Pythia. (PROSE: Transit)

Species-specific dreams
Time Lords sometimes dreamed of being able to fly or being a different sex or having a child. (PROSE: Human Nature)