The answer is "Increased production of serotonin and melatonin made them sleepy".
Serotonin and melatonin are the two hormones that control different human capacities, for example, rest, hunger and temperament. Serotonin, which is created in the body, is known as a neurotransmitter; this implies it is in charge of sending messages between nerve cells. Melatonin is a neurotransmitter like substance that assumes an essential part in directing circadian rhythms, which thusly control dozing designs, hormone discharge and body temperature, among numerous other human capacities.