How come the amount you sleep doesn't always relate to how tired you are?

Question

I can get by on around 6 hours sleep per night. However occasionally I feel so tired in the evening that I get an early night (around 10.00pm) - yet still only sleep maybe six or 6 and a half hours. Does your body really know how much sleep you need and do you always wake up when your body decides that it is rested enough (if there are no interruptions to sleep) Sometimes I can go back to sleep for another hour or so - but often feel more groggy as a result. What are the scientific facts please?

Answer 1

Here's something I cut'n'pasted from the link below, which I hope answers your question.

"Body's pacemaker

In humans the circadian pacemaker is located deep within the brain's hypothalamus, in the suprachiasmatic nucleus, where it helps the body keep time.

It controls a number of body functions and interacts with the mechanisms controlling sleep.

For most people, studies show that the pressure to sleep builds up throughout the day and peaks around 9pm-10pm.

At this time, the body's temperature starts to drop and lowers about one degree during sleep.

As it starts to rise, around 4am, the likelihood of waking increases.

In addition, the pineal gland, located deep within the brain, produces and secretes the chemical melatonin at high levels during the night.

A number of factors can affect melatonin secretion, especially many common medications and light. For example, a lamp turned off at bedtime can affect the stimulation of the pineal gland, and sunrise triggers the chemical process that enables a person to begin waking up."