What exactly is a charlie horse?!

What exactly is a charlie horse?

I get these all the time in my right calf when Im laying in bed. Whats up with them?

I think there are two types of ailments people are mixing up here (and I have had my share of both!) A charley horse generally refers to a deep thigh bruise caused by sudden strong contact to the quadriceps area (the front of the thigh). It can be extremely painful, inhibits your mobility and can last for several weeks depending on severity. I always thought the name was derived from someone who's been kicked in the thigh by a horse, which causes the same type of pain and "dead leg" condition.

Sudden painful contractions of the calf, hamstring, forearm, feet, hands, small of the back, etc., are just muscle cramps or spasms - not sure why people are calling them charley horses. They are very painful, but usually don't last more than a minute or two and will generally subside through stretching or on their own. I've always heard they occur when the muscles are overfatigued and dehydrated (and it may have something to do with loss of salt and minerals from the body).