Sometimes when we are under constant negative stress our hair falls out, turns gray or changes drastically from what it was before the stress. Trauma, grief or depression can have many adverse effects on your body and your hair can be an external reflection of what is going on inside your body.
If the stress is external and not controllable by you or your decisions, you may want to find a therapist, counselor, group or clergy-person who can help you not only cope with the stress, but also give you tools to overcome the stress.