John Lennon and Yoko Ono developed a reputation for public absurdism throughout their life together. One of their most outrageous stunts took place on April 1, 1970, when they sent out a press release stating that they had checked into the London Clinic to undergo sex-change operations.

Unlike the bed-ins or bagism, this wasn’t connected to any social commentary or political activism. It was simply an April Fools' Day joke. But as much as John and Yoko were laughing on the outside, they were undergoing an incredibly difficult time.

Earlier that year, Lennon had received a copy of Dr. Arthur Janov's book The Primal Scream, which advocated primal therapy, where childhood pain is dealt with by recreating traumatic incidents and expressing emotions that had been buried. Lennon -- whose father had abandoned him, causing his mother to leave him in the care of his Aunt Mimi and Uncle George -- was fascinated by the Janov's concept. In March, the couple invited the doctor to its Tittenhurst Park estate to work with him.

Toward the end of April, Lennon and Ono went to Los Angeles to further immerse themselves in the practice. But Lennon quickly became disillusioned by Janov. As former Apple Corps executive director Peter Brown wrote in his book The Love You Make: An Insider's Story of the Beatles, Lennon felt that Janov — like the Maharishi a few years earlier — had other motives: “[O]ne day Janov appeared at a therapy session with two 16mm cameras. John wouldn't even consider having his session recorded. ‘I’m not going to be filmed,’ John said, ‘especially not rolling around on the floor screaming.’ According to John, Janov started to berate them. ‘Some people are so big they won't be filmed,’ Janov said. Janov said that it was coincidental that he was filming the session, and it had nothing to do with John and Yoko's fame. ‘Who are you kidding, Mr. Janov?’ John said. ‘[You] just happen to be filming the session with John and Yoko in it.’”

Lennon later dismissed primal therapy as a passing fad. But its influence on Plastic Ono Band, most notably “Mother,” “God” and “Isolation,” would create the inextricable narrative for the album when it was released that December.

As Lennon was getting involved with Janov, the Beatles were breaking up. Lennon had told the other three members back in September that he was leaving, but the news hadn’t been made public. That changed on April 13, ten days before Lennon left for Los Angeles, when the press information accompanying the word of Paul McCartney’s self-titled solo debut confirmed the split.

But April 1, 1970, also holds a special place in Beatles history: Ringo Starr stopped by Abbey Road Studios to play along with the final orchestral overdubs Phil Spector was making on Let It Be. It was the last-ever Beatles recording session.