Schizophrenia
Schizophrenia is the most serious mental illness. Its main symptoms include hallucinations and delusions, which alter sufferers' perceptions of reality. Most hallucinations appear in the form of auditory voices, but other sensory hallucinations may arise as well. Three types of schizophrenia exist, each with distinct symptoms. Furthermore, research reveals brain differences among schizophrenics. While the cause of schizophrenia remains unknown, mental health professionals theorize that an interaction between genetics and stress may cause the disorder to surface.