Hi, welcome to the forum, there are hormones and neurotransmitters and receptors which play role in sleep and wakefulness.
Melatonin is one such
hormone and it appears to be the primary sleep-regulating
hormone of the body. It is secreted in relation with normal day/night cycles. It affects sleep itself, decreasing sleep latency, increasing sleep efficiency, and increasing the total sleep time. Melatonin acts on the melatonin receptors.