Sleep inertia is a well-established physiological phenomenon of grogginess and reduced alertness immediately upon waking, particularly when interrupted abruptly from deep sleep, making this claim a matter of common knowledge that requires no formal citation.
The claim describes the physiological definition and everyday observation of sleep inertia—the transitional state of grogginess upon abrupt awakening. As a basic, widely recognized aspect of human sleep physiology, it qualifies as common knowledge where formal literature citation is unnecessary.