So, basically, the reason why people use this term is to compare a sleeping baby to a person who slept exceptionally well. For example, a woman who got her beauty sleep feels happy, joyed, and well-rested, (like me!! ;)) so, she says that she feels like saying, "I slept like a baby." To kind of loosen up your fight, yes, many newborns sleep a lot, and all, and always wake up well rested, because apparently, they do not have a sleep limit! Please, if possible, rate this as brainliest answer, and if you are a girl who loves to dance, please visit the profile @idancesasha! I am trying to spread the word like many others! Help us get out there! Join our community! Please visit @idancesasha for more information!!!!! Thank you!!!