The common causes of sudden mood swings range from brain or other disorders to substance abuse and side effects of some medications. Mood changes may occur suddenly in a new environment or situation. Pregnancy and menstrual cycles also commonly cause mood swings as do hormones during adolescence. Other common causes of mood swings that may appear suddenly are cardiovascular and lung disease as well as seizures and strokes.
When a person suffers a stroke, brain damage may cause extreme emotions as well as changes in thoughts and behaviors. Sudden depression and anger may also be caused from the stroke sufferer's feelings about losing speech, movement or other physical skills. Seizures and sudden mood changes are related in that depression or irritability may occur just minutes before a seizure. Sudden mood swings in cardiovascular or lung disease may occur due to the brain receiving less oxygen and blood nutrients. The individual may suddenly feel disoriented or agitated and experience difficulty in concentrating.
During adolescence, the increase of sex hormones in the body may cause sudden mood changes. The experience of abrupt changes in mood or emotions typically don't last, though in females they may recur before each menstrual cycle. Premenstrual disorder (PMS) is a common cause of mood swings that may present as mild sadness or irritability about one or two weeks before the start of each menstruation cycle. Premenstrual dysphoric disorder is a more severe form of PMS with stronger mood swings typically occurring. Mood swings during or after pregnancy that appear suddenly are also common and usually due to hormonal changes.
In a stressful situation or new environment, it's common to experience sudden mood swings such as an easy going attitude than changes into anxiety or irritability. The chemical signals to the brain may change due to stress or fear in unfamiliar surroundings or new or difficult situations. Hormones such as adrenaline may create a sudden change in mood such as a "sped up" feeling and a rush of energy or urgency.
Some medications may cause sudden changes in mood due to changes the chemicals create when mixing with brain chemistry. Substance abuse, either of drugs or alcohol, is also a common cause of sudden mood swings relating to brain chemistry changes. Brain and mood disorders also cause mood changes of which a chemical imbalance may be at the root. Sudden shifts in mood are extremely common in bipolar disorder, which used to be called manic depression because of the cycles of elation contrasting with depressive episodes. People with rapid cycling or mixed episode types of bipolar disorders may especially be prone to sudden changes in mood.