It is reported that Lennon wrote this song at a Transcendental Meditation camp when he couldn't sleep.
The Beatles had gone on a retreat to study with the Maharishi Mahesh Yogi in Rishikesh, India.
After three weeks of constant meditation and lectures, Lennon missed his soon-to-be wife, Yoko Ono,
and was plagued by insomnia that inspired the song. He later said of it: "One of my favorite tracks. I just like the sound of it, and I sing it well."