Let's talk about something you probably haven't given much thought to: the posture you sleep in. I've helped many patients cure themselves of tension headaches by getting them to modify their sleeping positions.

The average person sleeps between 6-8 hours a night. Now, we just talked about the hazards of sitting at a desk in a slumped-over posture all day. We know that puts a great strain on the musculature.

When you turn in for the night, you probably don't fall asleep in a sitting position. Yet when most people sleep, they adopt a posture that is almost the same as when they're sitting in a chair. Their heads are down and shoulders are forward; they kind of tuck themselves up and in.

THE DANGERS OF SLEEPING IN POOR POSTURE

When you sleep like this, you're stretching your back out and bringing your chest, arms and neck in. As a result, you're causing these muscles to tighten up overnight.

Granted, you're not putting that much of a strain on these muscles, as they don't have to hold up your body and support it when you're asleep. However, your body adapts to the position you assume at night. So, if you sleep all curled up, the front of your body will begin to tighten up and the back of your body will begin to stretch.

That's just the opposite of what you're trying to accomplish during the day. You want to stretch the front of your body and tighten up your back. By lying on your side and curling up, you're tightening up the front of your body.

If you lie on your stomach - which is no good for your lower back - you're head's usually twisted to one side. While that will increase the flexibility of one side, it'll tighten up the other.

If you put your arm over your head while you're sleeping on your stomach, you'll stretch the front of your body. Unfortunately, you'll also cut off circulation there because you'll be pressing on the collection of nerves of the brachial plexus and the brachial artery, which supplies blood to the lower extremities.

So, sleeping on your side may be good for your back, but it's no good for neck, upper back, shoulders and chest.

WHY YOU SHOULD SLEEP ON YOUR BACK

What you need to do is sleep in a position that duplicates the kind of posture that you want to have during the day: shoulders back, head straight. Your ears should be in alignment with your shoulders, which should be in alignment with your elbows, which should be in alignment with your hip, knee and down through your ankle.

Obviously, the only way to maintain this positioning is on your back. Sleeping on your back represents a neutral posture; it represents a very straight posture that ensures that your body stays in alignment. If you can keep your body in alignment, it won't stretch or tighten up while you sleep.

A lot of people wake up with stiff necks, with their chests kind of tight and sore. Maybe their backs ache a little bit. The reason: They sleep all curled up, which causes their neck, back and shoulder muscles to stretch and tighten up.

WHY YOU TOSS AND TURN AT NIGHT

Do you toss and turn all night? If you do, it's because your muscles are tightening up as you sleep. What's happening is you're cutting off blood flow to them because you sleep all curled up. As a result, they get stretched out and tight. This causes them to become fatigued and spasm. These spasms cause the muscles to squeeze down on blood vessels, which deprives them of blood. Your tossing and turning is your body's way of repositioning itself so blood flow to these spasmed muscles can be restored. This is a never-endng battle for your body if you simply roll over and curl up into a different position (which you probably do!).

If you're sleeping on your back, however, you end this cycle. When you sleep on your back, it's important that you properly support your neck. However, by that I don't mean using a bunch of fluffy pillows. When you're sleeping on your back, using too many pillows - or pillows that are too thick - pushes your head down and forward. As you now know, this is a position you want to avoid. You want your head in the opposite position - up and back.

So use a small pillow. Sometimes a cervical pillow is good. Other times you can get away with using a small towel and kind of sticking it in the space behind the neck. Remember, all you want to do is support your neck - you don't want to push it forward.

LEARNING TO SLEEP ON YOUR BACK CAN TAKE TIME

You're probably thinking that getting used to sleeping on your back will be a difficult habit to incorporate. I won't lie to you, you're right. However, you need to give it a try because sleeping on your back goes a long way toward eliminating the cause of your tension headaches - stretched out neck and shoulder muscles and constricted chest muscles.

For a lot of people, sleeping on their backs isn't comfortable because they have such round shoulders and tight chests. So, when they lie on their backs, there's too much pressure on their upper bodies, which forces their shoulders back.

Yes, this could well be the situation for you. Sleeping on your back can be uncomfortable, even painful at first. However, as you begin to stretch out and assume a better posture, your shoulders and chest will loosen up. Before long you'll have no trouble sleeping on your back. And when you do, you'll find that you'll sleep much better and awake far more refreshed because your muscles won't be stiff.

CONSIDER GETTING A CERVICAL PILLOW

As I've said, you need to support your neck while you sleep on your back. You're probably wondering if I recommend a particular kind of cervical pillow.

There is no particular kind that will serve everybody equally well. The reason: Everybody's physically different. Some people have big necks; others have small necks. There is no "once size fits all" cervical pillow.

Therefore, I suggest that you check out different pillows at department stores, discount stores, medical supply stores, and pharmacies. A lot of times you're not allowed to return pillows you later decide you don't like. This may well happen to you, which, of course, will cost you a few extra dollars.

However, you need to experiment with a few to find the right one that will allow you to sleep properly and wake up pain-free. Consider it an investment to your health - it is!

I've got one last word about the subject of sleeping on your back.

When you do, try to keep your arms straight by your side and slightly away from your body. This will keep your chest muscles from tightening up. If you have shoulder problems, like a bad rotator cuff, it's even more important to sleep with your shoulders straight by your side and slightly away from your body because if you don't, you'll aggravate your problem by cutting off circulation.