NIHM defines this: A person's rhythms are synchronized when the interval between the time the pineal gland begins secreting melatonin and the middle of sleep is about 6 hours. (1) There are a number of therapies aimed at correcting the problem including lights, exercise, anti-depressants and melatonin. (See the Wikipedia entry.)The synchronization can be off in two ways: - a longer-than or a sho