sleep like a log
Also, sleep like a top. Sleep very soundly, as in I slept like a log, or She said she slept like a top. Both of these similes transfer the immobility of an object to that of a person who is sound asleep (since a top spinning quickly looks immobile). The first dates from the late 1600s; the variant is newer.
Words nearby sleep like a log
sleep apnoea,
sleep around,
sleep hygiene,
sleep in,
sleep learning,
sleep like a log,
sleep movement,
sleep off,
sleep on something,
sleep out,
sleep over