1970's Science fiction novel about alien abduction where both aliens and the men in black were paranormal projections

Question

I remember reading the paperback edition of this novel back in the 1970's whose cover showed a sleeping floating naked human underneath a flying saucer.

In the book researchers are finding evidence that alien abduction and visitation phenomena by both "aliens" and "men in black" are paranormal phenomena, projections from the subconscious of humans that take on physical form. For example, a virgin teenager recounts his sexual experience aboard a saucer with a supposed alien revealing his ignorance about female anatomy and knowledge of the sex act thereby supporting the notion that the experience is influenced by a human's cultural and personal context.

Answer 1

This is Miracle Visitors by Ian Watson:

John Deacon uses hypnosis to help his patients reach altered states of consciousness. One of his subjects, Michael Peacocke, is unusually susceptible and in their first session together, Michael recalls a "close encounter"--in both senses of the term--with an alien. Deacon, skeptical of the story, dismisses it as an adolescent sexual fantasy. But then strange things begin to happen and Deacon is forced to reconsider. Could UFOs be symbols projected from the collective unconscious? Are they messages from the biomatrix? Does the mind have the ability to project objects and people that are physically real...yet somehow illusory?

The cover you remember is this one:

In my youth (the 1970s) I was a huge Ian Watson fan, and I instantly recognised the book from your description. These days I find myself wondering if Ian Watson isn't a little too fond of being deliberately obscure, but his books are still essential reading for all fans of psychological science fiction.