In some bad situations which cause anger or sadness, i laugh or smile without being able to control myself! what is the problem? plz help. thank you

Anxiety: In primates there is what has been described as the "fear grin." i wonder if this is what you are describing. If you feel nervous, unsure, insecure etc, there can be a tendency to smile, grin, giggle, etc. Increasing our confidence that our feelings are valid is part of working on increased assertiveness. Therapy may help, you may also find helpful the book the four agreements by don miguel ruiz.