If your pineal gland secretes too much or for too long into the next day, you will have a tendency to be sleepy and not rested the next morning. Continuing melatonin production into the day can also result in depression and tiredness. If you do not get adequate sleep, mental acuity decreases too. Insomnia exists when melatonin levels are low or when it is produced at the wrong time. Melatonin is synthesized by the pineal gland from the neurotransmitter, serotonin.
Every human being produces their own melatonin.
It's a hormone that's secreted naturally by the pineal gland which is situated in the base of the brain's hypothalamus. This pea-size structure at the center of the brain is known as the body's clock. The pineal gland pumps out about 100 picograms per milliliter at night and goes to levels nine-tenths lower during the day. That's why melatonin has been nicknamed the night hormone. But, as the human body ages, the pineal gland calcifies and melatonin decreases.