Sleepless means passed without any sleep. A sleepless night, sleepless with worry, sleepless hours.
It attaches almost always to night: a sleepless night is the standard phrase, and sleepless nights in the plural is how people describe a period of worry. Applied to a place it means never resting: the sleepless city. Note insomnia, which is the medical term for the condition rather than the night; and that the compound has been in English, built exactly this way, since Old English.
1adjectivesleeplessPassed without any sleep.
“The baby's crying gave us another sleepless night.”
sleepless is a state of wakefulness.
Old English slaepleas is sleep plus -less, and the compound has survived unchanged for over a thousand years. English has kept a surprising number of these -less words intact.
Old English
slǣplēas
Middle English
slepeles
English, today
sleepless
From Middle English slepeles, from Old English slǣplēas; equivalent to sleep + less.
Etymology from Wiktionary, CC BY-SA