Dear Lucy: Lately, I've occasionally been waking up at night with a "Charley horse" in my legs. What causes this —Back in the Saddle

Dear Cowboy: : Lucy feels your pain! There's nothing worse than awakening from a sound sleep with one of those agonizing and disorienting muscle cramps! A "Charley horse" often affects one of the muscles in the calf and occurs in the middle of the night with no warning. When a muscle goes into a spasm like that, it locks in a contracted position, causing intense pain.

According to MIT Medical's sports medicine specialist, Shawn Ferullo, M.D., if you experience a Charley horse, immediately rubbing the muscle may help to relieve some of the initial pain. "For example, if you have a muscle spasm in your calf, rub the muscle from behind the knee toward the heel," he advises. But then, he says, it's best to get out of bed and try to stretch the muscle out. "Stretching is the best way to reduce the length of time the cramp may last," he explains, "although it may be painful at first."

Ferullo says a Charley horse may have many possible causes. "Sometimes it's a delayed reaction to a muscle strain during exercise," he notes, "but frequently it's caused by dehydration." Other potential causes might be a potassium deficiency, an electrolyte or mineral imbalance, a side effect of a medication, or some other medical condition.

Making sure you get enough fluids will prevent most Charley horses, Ferullo says. "Drinking a glass of orange juice in the evening may be the best idea," he notes, "because orange juice is also high in potassium." Lucy hopes this helps, but if these muscle spasms continue to be frequent, even after you increase your fluid and potassium intake, you might want to discuss other possible causes—and cures—with your clinician at MIT Medical. —Lucy