Final answer:
According to Emile Kraepelin, the two major groups of severe mental diseases are dementia praecox (schizophrenia) and manic-depressive psychosis (bipolar disorder), both characterized by distinct and debilitating symptoms as outlined in the DSM.
Step-by-step explanation:
The two major groups of severe mental diseases according to Emile Kraepelin, a pioneering German psychiatrist, are dementia praecox (now known as schizophrenia) and manic-depressive psychosis (now referred to as bipolar disorder). Kraepelin's classification laid the foundation for modern psychiatry's diagnostic categories. He identified schizophrenia as a disorder characterized by a disintegration of thought processes and emotional responsiveness, and bipolar disorder as a condition featuring alternating episodes of mania and depression.
According to Kraepelin's seminal work, schizophrenia symptoms may include hallucinations, delusions, and so-called "negative" symptoms like a flattened emotional state and loss of pleasure. Bipolar disorder is characterized by mood swings ranging from depressive lows to manic highs.
These major mental illnesses are detailed in contemporary times within resources like the Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychiatric Association, which lists symptoms and classification criteria updated through ongoing psychiatric research.