If you've ever woken up with an aching back after a night of tossing and turning, you know the value of a good night's sleep. On the other hand, if you've gone to bed feeling pain in your neck or back, you know how hard it is to get that good night's sleep. There seems to be a reciprocal relationship between sleep and pain. It's unclear whether chronic pain is caused by or is an effect of disturbed sleep. What is clear is that pain worsens when you are deprived of sleep. So it's essential to do whatever you can to make sure you sleep as well as you can. Here's some advice from Johns Hopkins.

Numerous studies show that chronic pain in the neck or lower back significantly affects how well you sleep. According to a recent study of 70 people reported in the Journal of Sleep Research, more than half of those with chronic back pain had insomnia severe enough to interfere with their daily functioning and to cause them distress.

Not surprisingly, the people who said they felt the most pain and were anxious about their health had the most severe insomnia. A growing body of evidence also shows that lack of sleep worsens pain. Recent findings from the Behavioral Sleep Medicine Program at Johns Hopkins show that frequently awakening for extended periods, such as when someone experiences insomnia in the middle of the night, impairs the natural pain control mechanisms that may play a key role in the development and exacerbation of chronic pain.

Finding the Right Mattress Good sleeping posture, like good standing posture, allows the body to follow the natural S-shape curve of the spine; by contrast, poor sleeping positions can strain muscles and ligaments and increase the risk of developing a compressed nerve and, consequently, back pain. Your mattress affects your sleeping posture.

One recent study in the American Journal of Physical Medicine and Rehabilitation examined sleep disturbances among 268 people who had chronic low back pain for at least six months. As you might expect, there was a significant increase in restlessness and light sleep once back pain set in at night. Unexpected was the finding that those who slept on a very hard, orthopedic mattress slept worse than those who used a mattress of medium firmness. This goes against the common belief that a hard mattress is better for back pain.

According to the Better Sleep Council (a manufacturer's group), a mattress is "good" if it supports the natural curves of your body, particularly the spine and knees. A mattress that is too hard, for example, will create gaps between it and your body. The result is pressure points that restrict circulation and interfere with sleep by causing the person who is asleep to move around to restore circulation. Also beware of an extra soft mattress. While it may feel plush, a mattress that is too soft may not give your back the support it needs.

The bottom line for a good mattress is comfort. While mattresses wear out at different rates, the Better Sleep Council suggests you may need a new mattress if you wake up with stiffness, numbness, aches, and pains; you had a better night's sleep somewhere other than your own bed (such as a hotel); or your mattress shows visible signs of overuse (it sags, has lumps, the interior is exposed).

Here are some tips for finding a mattress that is just right for you.

• Be sure your mattress supports your lower back and, to some degree, conforms to your body.
• Always "rest test" a bed before buying it -- lie down and stretch out to see how it feels. Some companies will let you try out a mattress at home. Be prepared to pay for this option, but it could be money well spent.
• If your mattress is in good shape but is too hard, a layer of foam or a feather bed may help.
• If you share a bed, you and your partner should try the mattress together to make sure there is enough room for both of you. A queen- or king-size mattress is recommended for two people.
• The box spring, which absorbs the wear and tear of nightly use, also should be in good condition, since it helps provide durability and support. Mattresses and box springs are designed to work together, so it's best to buy a matching set.