Pre-menstrual syndrome (PMS) refers to physical and emotional symptoms that occur before menstruation and lead to disruption in normal functioning in 3-4% of women. PMS is considered a normal menstrual phenomenon, but in severe cases called premenstrual dysphoric disorder (PMDD), it can cause mainly psychological symptoms. The document discusses diagnosing PMS by identifying symptoms that occur in the week before a woman's period and go away shortly after bleeding begins. Common symptoms include bloating, mood swings, breast tenderness, headaches, and food cravings.