1
general::
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.
American Heritage Idioms
2
general::
Phrase(s): sleep like a log [and] sleep like a baby
to sleep very soundly. • Everyone in our family sleeps like a log, so no one heard the thunderstorm in the middle of the night. • Nothing can wake me up. I usually sleep like a baby.
McGrawhill's American Idioms And Phrasal Verbs