inner thigh cramps

I am a 68-year old female who has suffered from these inner thigh muscle spasms for about 15 years.  Nothing seems to prevent them from striking, but I have observed that they are most likely to occur when I lie or sit in the same position for too long--e.g. trying to change positions in bed at night, in movie theaters during a long movie, and on airplane flights that are over one hour.  They cause excruciating pain and are immobilizing.  I have tried drinking water,  tonic water, and electrolyte-replacing drinks, but nothing works better for me than plain old pickle juice to lessen the duration whenever they strike.  I carry a little bottle in my purse whenever I go to a movie or travel by airplane.  I also sometimes keep a little cup by my bedside at night.  I have also discovered frozen pickle juice popsicles that can be consumed before bedtime to ward them off.  Just a couple of sips usually does the trick.