You wake from a deep sleep in a start. You may even jump up from the bed and howl. No, you're not transforming into a werewolf - you're experiencing the stabbing pain of a Charley horse.

Also called a nocturnal leg cramp, a Charley horse is a type of sudden, involuntary muscle spasm that usually strikes the calf muscle. The pain of a Charley horse can be severe, and is often described as cramping or stabbing or like the muscle has been twisted into a knot.

Everyone gets a Charley horse now and then, but risk increases with age. Pregnant women may also experience more frequent nighttime leg cramps, especially during the second trimester. Charley horse-like cramps may occur after strenuous exercise, when dehydrated, or if there is an imbalance of electrolytes.

How to ride out a Charley horse: First, flex your feet. If necessary - and if you are able to - stand up and walk off the cramp. Try jiggling your leg around or massaging the cramped spot. To relax the knot, run a warm bath or stand beneath a hot shower. Once the pain subsides, you can ice the area to reduce any incidental swelling.

How to prevent future flare-ups: During the day, drink plenty of water to prevent dehydration, which makes Charley horses more likely. Avoid caffeine-containing drinks in the evening. At bedtime, you can gently stretch your legs before tucking in. And un-tuck your sheets - that way, your feet are not compressed into contorted positions in the night.

While painful, a nighttime Charley horse often happens for no reason and is rarely cause for alarm or a sign of anything more serious. Occasionally, a Charley horse is linked to an underlying condition or to use of a medication. Talk to your doctor if nighttime cramps disrupt your sleep or if the cramps are accompanied by muscle weakness.

Amy Toffelmire