The Epworth sleepiness scale (ESS) is a widely used tool which has been validated as a measure of sleepiness.
Epworth Sleepiness Scale (ESS), an eight-item selfscored instrument that asks respondents to rate their propensity to fall asleep under a variety of routine daily situations on a scale of 0 to 3, with higher numbers signifying a greater chance of dozing; total scores may therefore range from 0 to 24. It has been suggested that a cutoff total score of 10 or higher indicates the presence of pathological hypersomnolence.
See the scale here: https://healthysleep.med.harvard.edu/narcolepsy/diagnosing-narcolepsy/epworth-sleepiness-scale
Walker NA, Sunderram J, Zhang P, Lu SE, Scharf MT. Clinical utility of the Epworth sleepiness scale. Sleep Breath. 2020 Dec;24(4):1759-1765. doi: 10.1007/s11325-020-02015-2. Epub 2020 Jan 14. PMID: 31938991.
Bhat S, Upadhyay H, DeBari VA, Ahmad M, Polos PG, Chokroverty S. The utility of patient-completed and partner-completed Epworth Sleepiness Scale scores in the evaluation of obstructive sleep apnea. Sleep Breath. 2016 Dec;20(4):1347-1354. doi: 10.1007/s11325-016-1370-8. Epub 2016 Jun 15. PMID: 27301400.