Actually, what you are describing is not a symptom of asthma.  To see what the symptoms of asthma are click here.  That said, emotions can be an asthma trigger.  Asthma triggers are things that can "trigger" an asthma attack.  To learn more about asthma triggers click here. 

There are some things you can do to help prevent emotions from effecting your asthma.  First, you should discuss this with your asthma doctor.  Second, you might want to learn and work on some relaxation exercises.  When you get emotional you can work on "relaxing" and this can help prevent this from causing asthma. 

Better yet, setting aside 5-15 minutes each day to concentrate just on relaxing your body might prevent emotional asthma altogether.  Trust me, I've tried this and it works great.

When I was a teenager I had asthma that was triggered similar to what you describe here.  Whenever I was tired, stress or anxious I'd have trouble breathing.  Fortunately I knew a great asthma nurse who taught me some great relaxation techniques.  One I mention in this post, although this post describes relaxation techniques better. 

You should also mention this to yoru doctor, because he or she might have some more ideas that might help.