A figure of speech to describe
sleep deprivation in the sense that a person cannot tell what time of day it is as soon as they wake up.
For an example, someone may wake up at 6:00 in the evening after sleeping all day, then they might believe it's 6:00
in the morning instead, because it's dark outside, and they must have slept for so long that their mind had went blank and forgot about the time of day.