Invasive emotions

I've started noticing a rather annoying trend in my living: my emotions can be bluffed by other people.  A particular incident recently highlighted it such that I can now look back and notice that it's occurred in the past.  

The incident was at the opening night of a play.  I attended primarily because a friend was playing one of the characters.  The play involved a number of Victorian era dances, and the actors made a great show of happy laughter and gaiety while they danced.  They did such a great job, in fact, that I found myself grinning like an idiot had to try very hard, rows back in the audience, not to.  My emotions reflected their acted emotions, despite my efforts to stop it.  It was very frustrating and unpleasant, but fortunately I don't think anyone noticed.  

Past events were things like suddenly laughing while being angry with someone, because they were acting silly and not taking my upsetness seriously.  I can now look back in and remember incidents where my emotions were bluffed into being different than they should have been, for similar reasons.  As I understand it, most people suffer incidents like this on occasion.  For me, it's rather disturbing because I have a hard enough time getting a sense for my emotions and how I'm feeling without someone else's changing them.  

I think I find this invasion of foreign emotions more concerning than most people as well, because it's hard enough to keep myself balanced and seem normal without the extra complication.  I already knew emotions would make things harder, but I certainly don't need help making them worse.  Perhaps I should address my complaints to my mirror neurons from now on.