Melatonin:A hormone produced by the pineal gland at night or in response to darkness. It plays a crucial role in sleep and circadian rhythms.
Serotonin:A neurotransmitter that has a wide variety of functions in the body. It's sometimes called the feel-good neurotransmitter because it contributes to wellbeing and happiness.
Circadian Rhythms: Physical, mental, and behavioral changes that follow a daily cycle. They respond primarily to light and darkness in an organism's environment.