John Lennon wrote this as a tribute to staying in bed
, which he liked to do even when he wasn't sleeping.
The song is discussed in the DVD Composing the Beatles Songbook
where they mention a theory that it's John's attack on "straight society," but conclude that the song IS about sleeping. John loved laying around in bed, sleeping, reading, watching telly or lovemaking. Didn't matter. He loved being in bed.
Maureen Cleave wrote of John Lennon: "He can sleep almost indefinitely, is probably the laziest person in England." She clarifies that she means physically lazy, not intellectually lazy.