Panic Disorder (PD) is a mental health condition characterized by sudden, intense episodes of fear, known as panic attacks, that occur without an apparent external threat. These episodes involve a rapid escalation of physical sensations, such as a pounding heart, shortness of breath, chest pain, and dizziness. Patients often believe they are experiencing a medical emergency, like a heart attack. The concept of this disorder as a distinct psychiatric illness is relatively modern, evolving from centuries of confusing these acute symptoms with physical ailments. The modern understanding of PD is largely attributed to a breakthrough in the mid-20th century that separated it from general anxiety.
Early Historical Context
Long before it was understood as a psychological condition, the symptoms of panic disorder were frequently miscategorized as purely physical problems, usually affecting the heart. A notable example emerged during the American Civil War when physician Jacob Mendes Da Costa observed numerous soldiers presenting with a specific set of complaints. Da Costa documented these cases in his landmark 1871 paper, describing a condition he termed “Irritable Heart,” also known as “Da Costa’s Syndrome” or “Soldier’s Heart.”
The soldiers experienced symptoms like chest pain, rapid heart rate, palpitations, shortness of breath, and fatigue, particularly after physical exertion. Da Costa’s detailed study of over 300 patients indicated a functional cardiac disorder. This meant the symptoms were present despite the absence of any observable physical disease of the heart. These early descriptions linked acute physical distress to an underlying, non-physical cause, but lacked the clear psychological differentiation that defines modern panic.
This syndrome was later reclassified as “neurocirculatory asthenia” or a form of “anxiety neurosis,” but the focus remained primarily on the somatic, or bodily, symptoms. The medical community struggled to distinguish these sudden, overwhelming episodes of physical distress from chronic, generalized apprehension. For nearly a century, patients exhibiting the signs of what we now call panic attacks were often grouped into a broad, undifferentiated category of anxiety.
The Defining Breakthrough of Donald Klein
The separation of Panic Disorder as a unique entity distinct from other anxiety states was achieved through the pioneering pharmacological research of psychiatrist Donald Klein in the 1960s. Klein’s work at the Zucker Hillside Hospital focused on using medication responses to differentiate psychiatric disorders, a technique he termed “pharmacological dissection.” This method provided an objective, biological way to categorize conditions previously defined only by subjective symptom descriptions.
Klein’s breakthrough observation centered on the effects of the tricyclic antidepressant imipramine. He noted that certain patients hospitalized for severe anxiety and agoraphobia were experiencing unexpected, sudden episodes of terror—the panic attacks—that seemed different from their baseline generalized anxiety. In his 1962 paper, Klein reported that imipramine selectively blocked the occurrence of these periodic panic attacks.
The drug demonstrated a specific mechanism: it suppressed the acute panic episodes but had no significant effect on the patients’ underlying generalized anxiety or apprehension. This pharmacological distinction provided the first concrete evidence that the spontaneous panic attack was a biologically separate phenomenon from generalized anxiety. Klein’s finding suggested that the two conditions had different underlying biological mechanisms, fundamentally changing how researchers and clinicians understood severe anxiety. He recognized that the intense fear and avoidance behavior (agoraphobia) seen in these patients was a consequence of the unexpected panic attacks, not the cause of them.
Formalizing the Modern Diagnosis
Klein’s research provided the framework for the institutional recognition of Panic Disorder, which was codified with the publication of the third edition of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-III) in 1980. This manual is the standard for classifying mental disorders used by mental health professionals globally. The DSM-III officially split the broad and often poorly defined category of “anxiety neurosis” into two distinct diagnoses: Panic Disorder and Generalized Anxiety Disorder (GAD). This separation was heavily influenced by the evidence that the two conditions responded differently to treatment, particularly imipramine.
The DSM-III established specific criteria for a panic attack, defining it as an acute, time-limited period of intense fear or discomfort accompanied by physical and cognitive symptoms. These symptoms include heart palpitations, sweating, trembling, shortness of breath, chest pain, and fear of losing control or dying. By formalizing these criteria, the DSM-III transitioned Panic Disorder from a research concept into a standardized, diagnosable condition. This cemented Donald Klein’s “pharmacological dissection” as the conceptual basis for its modern clinical identity.