IPA: //ˈsliːpləsli//
KK: /ˈsliːpləsli/
In a way that shows someone is unable to sleep or is experiencing a lack of sleep.
She tossed and turned sleeplessly throughout the night.
Sleeplessly → It is formed from "sleep" (from Old English *slæpan*, meaning to rest or be in a state of sleep) and "-less" (meaning without) and "-ly" (meaning in a manner). The word "sleeplessly" means in a manner without sleep or rest.
Think of being 'without' ('-less') sleep ('sleep') and doing something 'in that manner' ('-ly'). This helps you remember that 'sleeplessly' means acting without sleep.