If you're upset, you're unhappy or disappointed because something unpleasant has happened to you. You can also upset a situation and that means make the situation sort of go wrong. For example, after she died, I felt very, very upset. The whole, the accident really upset me. So if something upsets you, it makes you feel worried,. It makes you feel unhappy or it made you feel emotional. Let's have a look at Colin's dictionary and see what they say.