On April 27 1966, a new composition by John Lennon was recorded in eleven takes by The Beatles for their new upcoming LP. The song title was "I'm Only Sleeping". For some reason or another, this song was left in the can for the time being.
Two days later on April 29 1966, The Beatles returned to record another version of the song in Studio 3 of EMI Studios in London. There was a brief rehearsal with a bit of experimentation including adding vibes with an acoustic guitar and then recording a proper take with acoustic guitar, percussion and dual vocals by John and Paul.
Both the rehearsal and the song can be heard on the 3-LP/2-CD Apple "Anthology 2" set.
Eventually , take 1 from the 29th was not used but The Beatles decided to use the previous take 11 from the 27th instead and Lennon overdubbed his vocal on this instead of continuing with the "Anthology" version.