What would make me get upset for no reason at all?

Talk w/Psychologist: Most explanations for this have a psychological background, so should see an expert to help you identify what is going on and make recommendations as to how to best treat.

Always a reason: There's always a reason when we get upset -- even if it doesn't seem logical or obvious. I agree with dr. Alves that these reactions are usually psychological in origin. However, other issues like mood disorders, trauma, anxiety, and substance use/withdrawal, etc can make us more irritable or reactive. If you want help sorting it out, therapists and/or psychiatrists could work with you.