#sleep cycle

• Adenosine — A fundamental purine nucleoside formed by the structural binding of an adenine molecule with a ribose molecule. This essential component plays crucial biological roles as a structural element in major bioenergetic compounds, such as adenosine triphosphate (ATP), while simultaneously functioning in the nervous system as a neuromodulator with strong inhibitory effects regulating the sleep-wake cycle, and as an antiarrhythmic agent in emergency cardiology.
• To nod off — To fall into a light, short-duration, and superficial sleep; to doze or slumber for a brief period. Broadly, the verb describes the involuntary and transient transition from wakefulness to an incipient neurological relaxation, often occurring due to accumulated fatigue, boredom, or a soothing environment.