Somnolent
/ˈsɒm.nə.lənt/ adjective mediumA somnolent state or atmosphere is marked by heavy drowsiness, whether in a person or in a quiet place.
The somnolent hum of the classroom fan made it nearly impossible to stay awake during the afternoon lecture.
Memory Trick
Somnolent contains 'somn-,' the Latin root for sleep found in insomnia - somnolent simply means sleepy.