Cryptomnesia – (from the Greek. kryptos hidden, secret + memory mneme, memory) type of distortion of memories, which is characterized by the fact that people can't remember when it was an event, in a dream or reality, did he write the poem or did you just remember once read if he was on the concert of famous musician or have just heard conversation about it. In other words, forget the source of that particular information. Other people's ideas, someone else's creativity once perceived, after a while recognized as their own.
Cryptomnesia occurs when a forgotten memory returns, but not recognized as such by the subject, who believes it is something new and original. This is the memory offset, in which a person may falsely "remember" the creation of thoughts, ideas, song, or joke, not deliberately engaging in plagiarism but rather experiencing again the memory that recalls the inspiration.
Cryptomnesia, literally, hidden memory - this term was coined by psychology Professor théodore Flournoy (1854-1920) and is used by the author to explain the origin of experiences that people believe are original but which are actually based on memories of events they've forgotten. It is known that the brain apparently has an amazing ability to be stored deep in the subconscious, beyond the reach, all the information about each ever seen things and heard the conversation even after many years.
In the book "From India to planet Mars" , published in 1900 , Flournoy explores the phenomenon of psychic Catherine-Elise Muller. In 1894, he met a thirty-year-old SHOPGIRL whom he in his publications was called Helen Smith. Helen, 1892 participating in spiritualist séances and claimed that in a past life she was Marie Antoinette. In trance Helen with astounding verisimilitude acted out scenes from the life of the executed French Queen.
another cycle of reincarnation Helen was the daughter of an Arab Sheikh who married Indian Rajah. It was inserted into his speech the Sanskrit word, talked about the events that took place in India in the XV century, as if he was their witness.
Finally, Helen Smith told about his past life on Mars, describing in detail the local inhabitants, their houses, life, animals brought samples of Martian writing. She took up painting and painted pictures of Martian life.
In the published book "From India to planet Mars" claimed that the Martian language of Helen Smith - a distorted French, Arabic sayings borrowed from a doctor in the Smith family, who studied Arabic language and that historical information (sometimes incorrect) taken from an old historical work.
a year after released book, Helen Smith has talent. Going into a trance, she took up brushes and painted pictures on religious themes. Her paintings are a vivid example of art Brut - art Amateurs, has a spontaneous nature and not dependent on cultural traditions. 
Carl Gustaf Yung considered cryptomnesia in his dissertation "On the psychology and pathology of so called occult phenomena" (1902) and in the article "Cryptomnesia" (1905), suggesting that this phenomenon existed in the work of Friedrich Nietzsche "thus spoke Zarathustra".
“an Interesting example is cryptomnesia, or "hidden memory". For example, the writer works by developing in strict accordance with a predetermined plan the storyline or the action of the story. Suddenly, he suddenly digressed. Maybe he came to mind a fresh idea or a new image, or even plot device. If you ask a writer what caused this deviation, he will not be able to explain. He might not even notice the change, although the generated material is quite new and were not known to him earlier. At the same time, in some cases it is possible to prove the existence of striking similarities written from someone else's work, which he believes are totally unfamiliar.
I found a stunning example of its kind in the book Nietzsche's 'thus spoke Zarathustra", where the author reproduces almost word for word an incident described in one of the ship log in 1686. By happy coincidence, I read this sea story in the book, published, if my memory serves me, in 1835 (for half a century before Nietzsche took up the pen). Finding a similar description in Daniel, I drew attention to the unusual style, different from common Nietzsche. I am convinced that Nietzsche, too, fell into the hands of the old edition, although it was not referred to him. I wrote to the sister of Nietzsche, then surviving, and she confirmed that he had read with his brother this book when he was eleven years old. Apparently, Nietzsche, and could not imagine that he engaged in plagiarism. I am sure that the story fifty years later, suddenly fluttered into his mind. Similar to the situation in which the person is not aware, typical true memories. Almost the same can happen to a musician. Heard them in my childhood village chant or popular song he can, as in adulthood, to insert as a leading theme to compose a Symphony. It is the idea or image came back from the subconscious to the conscious mind.” 
In his work “the Concept of the collective unconscious” Yung wrote that “to define the collective unconscious is not always easy. It is not enough to point out the often obvious archetypal character of the manifestations of the unconscious, for they can be owe their origin to the acquisition of language and education. This should be excluded cryptomnesia, in some cases, almost impossible.” 
1. Gerstein, M. the Journal "Secrets of the twentieth century, No. 12, 2016
2. Holtzman E. Pierre Janet, Sigmund Freud and multiple personality // "Science and life", №6, 2002.
3. Carroll R. T. Cryptomnesia // the skeptic's dictionary: a collection of incredible facts, amazing discoveries and dangerous beliefs = The Skeptic''s Dictionary: A Collection of Strange Beliefs, Amusing Deceptions, and Dangerous Delusions. — M.: "Dialectic", 2005. — P. 252.
4. Richard Noll. The secret life of Carl Jung. Series: Contemporary psychology. Publisher: Refl-Buk, Vakler, 1998
5. Yung K. G. essays on the psychology of the unconscious. M.: Kogito-Tsentr, 2010. 352.
6. Jung, C. G. Man and his symbols. Under the General editorship of Sirenko S. N. - Moscow : Silver threads, 2002. - 296 p.