Now among the 3 reactions, which would you think would be the easiest for you to control? Not suprisingly, it should be our behaviour. By controlling how you behave towards an event, it could affect the other two, which will in turn help you to look towards the bright side and start channelling your thoughts and energy towards resolving the problem or bracing the challenge. So instead of trying to control your emotions and thinking, do it the other way by first behaving the right way.
You might want to call it "acting". Act what you feel should be the right way, and your mind and emotions would naturally attune to the behavioural change. In fact, "acting" is a powerful way to build your self confidence, as you start visualising and act the way you want to be. Even if it seems superficial in the beginning, it will come natural once your self confidence kicks in.