sleep has 10 distinct synonyms spread across 5 of its 6 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is wake.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a natural and periodic state of rest during which consciousness of the world is suspended
“he didn't get enough sleep last night”
a period of time spent sleeping
“he felt better after a little sleep”
euphemisms for death (based on an analogy between lying in a bed and in a tomb)
“she was laid to rest beside her husband”
be able to accommodate for sleeping
“This tent sleeps six people”
Synonyms, antonyms and the broader and narrower relations for sleep come from Princeton University’s WordNet. Full sources and licences.