I have no idea im sorry. i just thought i could help with an answer =)
maybe because DID can involve dissociation from your emotional state? like it's separate from the rest of you or you don't notice it? but yeah, the words you're looking for are 'indifferent' and, moreso, 'apathy'. Apathy can be alarming or horrible or neither. Drugs definitely affect this sort of thing. If you can try to lay off them for three weeks, your systems should have enough time to detox and get up and running properly again => emotions back! Which may or may not be pleasant... But deal with that when you get there :)
Also, Showing no emotion could be called 'acting'. Just for completion's sake..
Sociopaths carry this trait. But its really just a " no remorse" or empathy thing. I've met a few in my day. Scary as marriage.
Apathy I believe it is.
Read up on emotional intelligence. If that doesn't ring any bells, then look into psychopathic(sociopath sounds nicer lol) personality disorders. The DSM-IV has some info on it, but the DSM-5 is prob going to have a more accurate picture of it(not out yet, but some info is available). Not everyone is the same, as long as you aren't gonna go on a killing spree, you will be fine. Some people are not as emotional as others. Not a big deal, but if you feel it's going to get out of control, then talk to someone you trust(or a "Professional") for advice on what you might be able to do to deal with it. G'luck and realize that some of the drugs out there are not meant to be used without some type of guidance(SRS!), and some of the newer ones should not be used AT ALL(SRS SRS!!). Also, learn to mimic (feelingsconcern) a little bit lol, or people start thinking you're too strange and start to stay away. No one wants a dead fish as a friendlover. Again, g'luck!