This is definitely odd that so many people have this going on. Mine started just after I had my first child and seems to be closely related to sleep deprivation. My oldest is 22 yrs old so this has been going on for a while just not terribly frequently thankfully. Its driving me nuts today which is what got me looking for answers. Mine has always been on my right side and is an area closer to the size of my fist. It lets up for a few seconds when I stretch.