Hi! If you're seeing a therapist, this is a great thing to work on with him/her. Emotional flatness can be a symptom of something else (depression, for one) or can be the result of medication. It can also be a learned response.

For example, a parent says something sarcastic but the child doesn't realize it's sarcastic. The child laughs. The parent rages at the kid - how can you be so stupid?! Don't you ever laugh at me like that again. So what does the kid do next time? Nothing. The kid equates laughter with being yelled at, belittled or worse.

The (only) good thing about learned behavior is that they can be unlearned. It does take a great deal of work though. You need to be willing to have someone (usually a T, but could be a good friend) call you on your emotional reponse (either it's missing or not matched up with your words). You can then try a different response. It will feel forced and silly and uncomfortable. But all learning is this way.

Of course, if it's a result of untreated or badly-treated depression, talking to a psychiatrist is always a good option.

Best of luck to you.