Staying awake for 21 hours makes young healthy people feel about 2.4 times more tired and sleepy than when they're well-rested, according to standard measurements of fatigue and sleepiness.
Scientific Claim
Sleep deprivation for 21 hours significantly increases subjective fatigue by approximately 141% and sleepiness by 172% in young healthy adults, as measured by standardized fatigue and sleepiness scales.
Source Excerpt
“Under placebo KSS and FAT progressively increased in all subjects except FAT in one, terminally at 4 a.m. by 172±17% and 141±23%, significant at each versus every preceding time point (p12<0.0002, t12>3.2, vs. baseline and all other comparisons; Table 1).”
Evidence from Studies
Supporting Studies
Single dose creatine improves cognitive performance and induces changes in cerebral high energy phosphates during sleep deprivation
The study measured subjective fatigue using the Karolinska Sleepiness Scale (KSS) and the inverted Samn & Perelli Fatigue score (FAT) and found significant increases after 21 hours of sleep deprivation compared to baseline.