Focus on the facts Ma'm just the facts.
When the brain can't find an answer or solution it will make something up. We've all been there; your boss calls you into the office and your brain immediatley makes up a story about you being in some sort of trouble.
To over come this, you must train yourself to focus on the facts of the situation. FACT - your boss calls you into his office. ASSUMPTION - I'm in trouble.
Get rid of the assumption and focus on the facts.
With a little practice you can strengthen this muscle just like any physical part of your body.