Diffuse Esophageal Spasm?

My son who is 12 has a problem of getting food or large pills stuck in the mid-esophagus area.  He has been like this since he has been old enough for solid foods.  At first we thought he was choking but experience has taught us that he just has something stuck in his esophagus and not to panic.  For example, just last night a piece of pork shop became stuck in his esophagus.  He then can't swallow and he drools.  He also gags.  Drinking water doesn't help because it comes right back up.  This went on for several hours then finally, it went down and he was fine.  Although the incidents do not happen that often I would like to know what is going on here.  I recently did some research on the internet and came up with diffuse esophageal spasm which closely resembles what is going on with him.  I took him to the emergency room once when he got a pill stuck and the doctor suggested that he may have a crooked esophagus.  Could this be the case or could it be this diffuse esophogeal spasm?