That awful empty sinking feeling inside when a play you were in is over and you know it'll be really hard to see anyone from the cast outside of the show. Also applies when it's the last show of the year and the seniors are graduating soon.
Common symptoms also include desire to cry, denial, and musical numbers or lines popping into your head at random times.
Common treatments include indulging in junk food and seeking the next opportunity to be in a play so you can set yourself up for more withdrawal later.
*cries* I just got back from the Rent cast party, and now I'm going through such awful theatre withdrawal! Where's the chocolate and the latest issue of Variety?