Sedation
This is a forced state of drowsiness or sleep.
Sedation is the reduction of irritability or agitation by administration of sedative drugs, generally to facilitate a medical procedure or diagnostic procedure.
Drowsiness and Sleepiness
The terms drowsiness, sleepiness and [hypnagogic period][2] are often used to describe the same thing in the general domain, but but in the scientific domain there are important neurophysiological and psychophysiological differences.Hypnagogic period
This is the neurophysiological and psychophysiological transition period from the wake to sleep state.Drowsiness
This is the state of the transition period from the wake to sleep state **that can be objectively measured**, for example, by EEG (please see [Hori et al., 1994][3])Typical tests that describe the quality and quantity of the drowsyness are Multiple Sleep Latency Test (MSLT) and Maintenance of Wakefulness Test (MWT) (Doghramji et al., 1997).
Sleepiness
This is the **subjective state of the subject/patient**. It can also be qualified and quantified, but only by rating scales such as the [Stanford Sleepiness Scale (SSS)][6], the [Epworth Sleepiness Scale (ESS)][7] (See also [Johns, (1991)][8]), the Karolinska Sleepiness Scale ([Åkerstedt & Gillberg, 1990][9]), etc.References
Åkerstedt, T., & Gillberg, M. (1990). Subjective and objective sleepiness in the active individual, *The International Journal of Neuroscience*, 52(1-2): pp. 29–37)DOI: [10.3109/0020745900899424][10] PMID: [2265922][9]
Doghramji, K., Mitler, M. M., Sangal, R. B., Shapiro, C., Taylor, S., Walsleben, J., Belisle, C. Erman, M. K., Hayduk, R., Hosn, R., O’Malley, E. B., Sangal, J. M., Schutte, S. L., & Youakima, J. M. (1997). A normative study of the maintenance of wakefulness test (MWT), Electroencephalography and clinical neurophysiology 103(5): pp. 554–562.
DOI: 10.1016/S0013-4694(97)00010-2 PMCID: PMC2424234
Hori, T., Hayashi, M., & Morikawa, T. (1994). Topographical EEG changes and the hypnagogic experience. In R. D. Ogilvie & J. R. Harsh (Eds.), Sleep onset: Normal and abnormal processes (pp. 237-253).
DOI: 10.1037/10166-014
Johns, M. W. (1991). A new method for measuring daytime sleepiness: the Epworth sleepiness scale, Sleep 14(6): pp. 540-545
DOI: 10.1093/sleep/14.6.540 PMID: 1798888