Paul McCartney still can't believe he and his fellow Beatles survived the swinging sixties - because they took so many drugs and often couldn't even think straight.

The Yesterday singer admits the Fab Four overused narcotics during their heyday and often fell asleep recording musical masterpieces they composed while high.

In an exclusive interview with Entertainment Tonight, he says, "(We were) overdoing substances and really getting crazy, as we all were... (We'd be) falling asleep - the kinda thing when you can hardly get your head off the pillow. You go, 'Woah, I'd better get my head off this pillow.'"

However, one drug-induced state inspired McCartney to write Beatles classic Let It Be.

He adds, "I had a dream, where my mother, who had been dead, by then, 10 years came to me in the dream and was very sort of helpful and very calming, and it was lovely just to see her... and she said, 'Don't worry about it... Let it be.'

"I went, 'OK', and I felt so good... and I woke up and wrote Let It Be. I thought, 'That's a good idea for a song.'"

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(This news article provided by World Entertainment News Network)