A dream was a series of sensations in the mind during sleep, forming their own virtual reality. (PROSE: Set Piece) Dreams could allow revelations, communication and insights into the psychology of an individual. (TV: The Time Monster, Doomsday, PROSE: The Also People) It was illegal to dream on Colony world 4378976.Delta-Four, just as it was to recount stories or tell lies. (PROSE: The Stealers of Dreams) Even cybernetic intelligences, such as the robot Handles, were capable of dreaming, or at least so the Eleventh Doctor believed. (TV: The Time of the Doctor) When he was being upgraded the Doctor even asked the Cyberiad if he would dream once it consumed him. (COMIC: Supremacy of the Cybermen)
The Kyropites of YT45 induced dreams which appeared to be absolutely real but slowly killed the dreamers. Erimem and Peri Brown each experienced Kyropite-induced dreams, but were rescued by the Fifth Doctor. (AUDIO: The Mind's Eye)
Dream crabs pacified their prey by placing them within a telepathically-induced dream state while consuming their brains. They died if their prey escaped their dreams, but could create dreams within dreams to prevent this from happening. The Twelfth Doctor, Clara Oswald, Shona McCullough, Ashley Carter, Rona Bellows and Albert Smithe experienced shared dream states induced by dream crabs, but escaped with the aid of a dream version of Santa Claus. (TV: Last Christmas)
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 pressured by Louise Marlowe to tell her everything she knew 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 being 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 one's future, another's future or a possible future.
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 the Master 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) Hex dreamed of a group of people performing an operation on a doll with no eyes. (AUDIO: Night Thoughts)
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)
At one point, Vastra arranged a psychic "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. However, despite no longer being in a dream-state, River managed to keep the connection it established between her and Clara to appear to her as a ghost-like figure and guide her on Trenzalore. It is unclear how River was able to enter the dream at all being a data ghost. (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 through 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)
According to one account, which may itself have been a dream, Zoe Heriot dreamed of her adventures with the Doctor after going into a coma which lasted twenty-three years. (PROSE: Dream a Little Dream for Me) Zoe 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, AUDIO: Fear of the Daleks)
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)
Fitz Kreiner, after his mind and personality were briefly mixed up with the Eighth Doctor's on Estro, had a dream in which he rubbed buttocks with the Doctor in the TARDIS control room while a herd of zebras passed through on their way to Trix's bedroom, after which their bodies began to merge together. (PROSE: Halflife)
The Twelfth Doctor, Clara Oswald, Rona Bellows, Professor Albert Smithe, Shona McCullough and Ashley Carter were trapped in a shared dream by dream crabs from across time and space. Their minds reacted by bringing them all together at a research station in the North Pole where the part of their minds that had surrendered were represented by copies of themselves with dream crabs on them and their subconscious fighting back was represented by Santa Claus. Inside the dream, Clara was put into another dream where she dreamed Danny Pink was still alive and she was with him until the Doctor entered that dream and convinced her to wake up from it with the help of Danny. In the shared dream, the Doctor convinced the others of the truth using their manuals after figuring out that Santa wasn't real then helped them apparently wake up. However, he later realised they were all still in the dream as there were four people with crabs yet only four instruction manuals and he and Clara had seen Santa before coming. Smithe was killed when he was attacked by his dream crab self, meaning he died in reality, but the Doctor and the others escaped by dreaming Santa flying them home. The symbolism of the group escaping from where they were trapped in the dream allowed them to wake up one by one in the real world, causing the dream crabs to die until only the Doctor and Clara were left. The Doctor believed he woke up but ended up in another dream which represented his regrets regarding Clara as he dreamed he came back sixty-two years late before another appearance by Santa caused him to realise the truth and wake up for real. As Clara didn't want to wake up on her own, the Doctor removed the dream crab from her and, remembering his dream, invited her to rejoin him as a companion. (TV: Last Christmas)
The Doctor's dreams
After teaming up with all of his incarnations to save Gallifrey at the end of the Last Great Time War, the Eleventh Doctor talked about his dreams. He explained that Clara once asked if he had dreams to which he told her that he did, with one such dream being about him trying to go to where his life was leading him. Clara would laugh and say he wasn't going anywhere. However, the Doctor explained that he had a new purpose, finding Gallifrey "the long way round". The Doctor imagined himself looking at his home planet with all his past incarnations. (TV: The Day of the Doctor)
The Twelfth Doctor shared dreams with Clara Oswald and four other people due to dream crabs, but after apparently awakening, he ended up in another dream where he found he came back to Clara sixty-two years after he left her and never returned for her. The Doctor regretted never seeing her before then and Santa Claus appeared to ask him what he'd do to make it right, causing him to realise it was another dream and wake up for real. He then found Clara in the same way he did in the dream but young again. He asked her to rejoin him as his companion. (TV: Last Christmas)
The Twelfth Doctor claimed that every human being had the following dream during their lifetime. In this dream, one woke up in their bedroom but felt as though someone else was there in the dark. While the dreamer tried to convince themselves that they must be alone, they were unable to shake the feeling that there was something in the room. And later, they felt a hand grab their ankle from underneath the bed. (TV: Listen)