Consciousness is our awareness of the world around us and of what's happening inside us, like thoughts, feelings, hunger, or tiredness.
Sleep and wakefulness are two different states of consciousness: awareness is reduced in sleep, but the brain still processes some sounds and sensations.
The sleep-wake cycle is a circadian rhythm, a biological rhythm that follows an approximately 24-hour cycle.
Melatonin is released as it gets dark, signaling the body that it's time to sleep.
Jet lag and shift work disrupt the circadian rhythm by putting the internal clock out of sync with the outside world; daylight gradually resets it.
Key terms
consciousness
Awareness of the world around you and of what's happening inside you.
states of consciousness
Different levels of awareness; sleep and wakefulness are two distinct states.
circadian rhythm
A biological rhythm that follows an approximately 24-hour cycle, such as the sleep-wake cycle.
melatonin
Hormone released as it gets dark, signaling the body that it's time to sleep.
jet lag
Circadian rhythm disruption when your internal rhythm hasn't yet adjusted to a new time zone.
shift work
Working overnight hours, which forces being awake and asleep at times the body isn't used to.