Sleep is not a static condition, but actually a fluid condition with changes occurring through the sleep period. These stages demonstrate different brain wave patterns. Rapid eye movement (REM) is the period of sleep when we dream. There are about five periods of REM during the night. The deepest periods of sleep, stages 3 and 4 occur earlier in the night. It is the deeper phases of sleep which decrease in duration as we age.
To find the cause of insomnia, find out whether it is initiation maintenance of sleep that is the problem. Look for the more common insomnia precursors such as stress related factors. An increase in caffeine consumption is something to take a look at. Coffee, tea, and colas could be the culprit. Shift workers often have a problem resetting their biological clock to deal with a variable schedule. The use of alcohol as a sedative before bed can have the opposite effect resulting in further impaired sleep.
A common cause of insomnia in people over the age of 35-40 is deficiency of the hormone melatonin. Melatonin is the hormone released by the pineal gland that induces drowsiness, and enables the body to enter the deep sleep patterns characteristic of youth.