That is basically the definition for psychological diseases. So let's take mood swings, for example. Do you think that mood swings can be a psychological disease? Mood swings is a thing that we all have, once in a while, have suffered from, especially in adolescence. Your mood goes from a very high happy level to a low sad level, right? But no, it's not a psychological disease. But it may become a factor for a certain type of psychological disease, such as bipolar disorder