The Fundamentals of Sleep-Wake and Consciousness

Consciousness remains one of the most elusive and fascinating mysteries of life. Every day and night, human beings and other species naturally transition between consciousness and unconsciousness, i.e., between wakefulness and sleep. A disruption of this process can result in sleep-wake disorders, such as central disorders of hypersomnolence, parasomnia, or insomnia. However, the alteration of consciousness or presence of unconsciousness is not limited to sleep-wake cycles but includes other prominent examples such as anesthesia, disorders of consciousness (e.g. due to brainstem lesions), epilepsy, and neuro-psychiatric disorders (e.g., encephalitis or psychosis).