How to tell between mental illness and normal emotions?

VAGUE ANSWER: Real departures from reality in one's thinking and behavior. Very intense emotions that last a long time. Anything that disrupts daily living, work and fun repeatedly is a candidate to be called mental illness. Major changes in one's behavior, demeanor, or spirits should rouse suspicion of illness. If this is a real concern, why not see an expert, give enough information & get an opinion?