What Causes Muscle Spasms In The Right Leg?

Question: I have had muscle spasms usually on the outside of my right leg occasionally for years. Once in a great while I have had SEVERE muscle spasms in the insides of both my thighs. But it has been several years since the last time I had one of those. But on Labor Day this year (September 4, 2017), I had a SEVERE episode of muscle spasms in the backs of the thighs of both of my legs. I was sitting in partially reclined position in a power recliner at my sister's house, one which was new to them and that I had never sat in before. I didn't have my legs all the way even with my body, but down at approximately a 45 degree angle. I usually have my legs about that position with a large pillow under my knees. But the chair I was sitting in at the time is the only thing that is different. I had had a meal earlier that day that had about 600 or 700 mg of sodium in it and probably hadn't drunk enough water. I had pinched my skin to see if I was dehydrated and it only looked like a little bit of skin stayed up for only a second. My question is: What do you think might have brought this on and what can I do to prevent these from happening again? It really scared my sister and brother-in-law. They'd never seen me have one of those, and I yelled pretty loudly with the pain. As soon as I was able to, I transferred out of their new chair over to their soft stuffed leather couch which I had sat in many times without a problem, and had no further trouble that day, or since. I would sure appreciate some advice on this. Thank you.

OK, thank you. It was extremely painful, would subside for a minute or two but then coming back and it alternated between one leg and the other, with the muscles kind of rippling painfully. I couldn't stand up because it was so painful. I find taking a tablespoon or so of regular mustard tends to help with the less painful ones but this one was so bad it took two separate doses of it and, as soon as it finally subsided, getting out of that chair and onto a sofa that was softer to finally end the episode. It went on for half an hour or so. Had I not had the mustard, it would probably have gone on much longer. I was at my sister's house, which is a two-story house with the bathroom upstairs, so a shower would not have been practical. Heat might have helped though. Didn't think of that. Electrolyte imbalance was one thing my sister mentioned after looking this problem up on the internet. I'm glad to see that you agree. What would be the best way to get electrolytes back in balance in my system?

OK, that helps. Thank you very much for your help, doctor. Have a great day. XXXXXXX Storm
YYYY@YYYY