Your condition should not dictate your mood. If you allow your condition to dictate your mood, overtime your body will adjust so much that it will be very difficult for you to alienate your mood from condition.
I understand we all go through tough times at one point in our lives. Everybody knows this... mind you, a condition of distress can deform our facial expression.
If you are going through a condition of distress or annoyance - called trouble, force yourself to smile. It will go a long way in helping you to put your face in good shape.
In addition, it is not compulsory your smile is seen on the outside. Smiling within you can even help you in a bad situation, eventhough the smile may not show on your face.
So, do not allow bad situation take away your happiness.
Stay happy