Sometimes people just crack up; sometimes one's past--along with self-inflicted abuses interspersed over the course of said past--manifest in forms of personal behavior widely considered inappropriate by more prudent, emotionally balanced members of civil society. Alcoholism is one of the numerous self-destructive avenues to achieve a lasting mental and emotional state of impaired perception.
The website Addiction Intervention describes effects of alcoholism translating into a loss of memory, difficulty with learning, poor judgment and loss of inhibition, crying jags, bouts of hysteria, and anger. While professional medical treatment may "show at least some improvement in brain structure and cognitive functioning within a year of abstinence," lingering damage from addiction is not uncommon.