Doctor Who's regenerations were modelled on bad LSD trips, internal BBC memos have revealed.
The Doctor's transformations were meant to convey the "hell and dank horror" of the hallucinogenic drug, according to papers published on the BBC Archive.
Regenerations were introduced in 1966 to allow writers to replace the lead actor. New Doctor Matt Smith is the 11th Time Lord.
The papers also reveal the difficulties of bedding in a new Doctor.
In an internal memo dating from 1966, producers outlined how the original Doctor, William Hartnell, would be transformed for his successor Patrick Troughton.
It also tackled the "horrifying experience" of the regeneration.
"The metaphysical change... is a horrifying experience - an experience in which he relives some of the most unendurable moments of his long life, including the galactic war," it said.
"It is as if he has had the LSD drug and instead of experiencing the kicks, he has the hell and dank horror which can be its effect," the memo added.
Discussing his appearance, the document stated: "His hair is wild and his clothes look rather worse for wear (this is a legacy from the metaphysical change which took place in the Tardis)."
The documents also reveal how new Doctors have faced hostility from viewers.
Some members of the audience felt Troughton "exaggerated the part".
"Once a brilliant but eccentric scientist, he now comes over as a half-witted clown," said one viewer.
Another told the BBC's Audience Research Department: "I'm not sure that I really like his portrayal - I feel the part is exaggerated - whimsical even - I keep expecting him to take a great watch out of his pocket and mutter about being late like Alice's White Rabbit."
His successor Jon Pertwee fared a little better in 1970, although a research report following his first appearance declared: "Reaction to this first episode of the new Dr Who series can hardly be described as enthusiastic."
Tom Baker's debut also drew much criticism.
"General opinion was that the new Doctor Who is a loony - he is an eccentric always, but the way it was presented made him stupid," said one viewer.
And in 1984, Colin Baker proved to be a turn-off, with one viewer finding him "too stern" and another "too aggressive".
Reaction to Sylvester McCoy's debut in 1987 was even worse. His "approval rating" was considerably lower than Colin Baker's, although the reception given to his sidekick Mel, played by Bonnie Langford, was worse.
Roly Keating, the BBC's director for archive content, said: "The whole idea of regenerating the Doctor was a flash of genius that's kept Doctor Who fresh and exciting for 47 years now.
"As we welcome Matt Smith and Karen Gillan into the Tardis, it's the perfect moment to remember his predecessors and also to celebrate the work of the BBC Archive in preserving these documents and photographs for future generations."