Alcohol interferes with a person's perception of reality and ability to make good decisions. This can be particularly hazardous for problem-solving and a decision-making experience. The short-term effects of drinking include altered perceptions and emotions and impaired judgment.
As said above, alcohol is a drug that depresses the brain. We all know the cheeriness that can come with the first drink, but alcohol can actually cause severe depression. 'Letting go' is an effect which can initially be pleasant, can get some of us into difficulties, because when our petty or angry side gets exaggerated by alcohol, friendships or marriages can be threatened.
Alcohol is a powerful nervous system depressant, that's why it is so relaxing. However, the depression of the nervous system, and hence the emotions, lasts much longer than the pleasurable effects.
Another major emotional problem which alcohol leads to is irritability, or anger management problems. This has a number of causes, but probably the most immediate is from low blood-sugar levels.