Did Lennon understand Tomorrow Never Knows?

John Lennon first discovered The Tibetan Book of the Dead in the Indica Bookshop, hang out for London's grooviest tambourine shakers in the mid-60s. 

John began to scan the shelves. His eyes soon alighted upon a copy of The Psychedelic Experience, Dr Timothy Leary's psychedelic version of the Tibetan Book of the Dead. John was delighted and settled down on the settee with the book. Right away, on page 14 in Leary's introduction, he read, 'Whenever in doubt, turn off your mind, relax, float downstream.' He had found the first line of 'Tomorrow Never Knows'. 

Many Years From Now Barry Miles

Did Lennon understand what he was singing?

Though intellectually curious, Lennon always cheerfully conceded that his research tended to be haphazard. In Anthology, George Harrison dismisses Lennon's knowledge of Indian mysticism: 

I am not too sure if John actually fully understood what he was saying. He knew he was onto something when he saw those words and turned them into a song. But to have experienced what the lyrics in that song are actually about? I don't know if he fully understood it.

George Harrison, Anthology

That said, those words over that drone have an undeniable power in one of his Lennon's finest songs.

Where did the title Tomorrow Never Knows come from?