Panic attacks involve sudden feelings of terror that strike without warning. These episodes can occur at any time, even during sleep. People experiencing a panic attack may believe they are having a heart attack or they are dying or going crazy. The fear and terror that a person experiences during a panic attack are not in proportion to the true situation and may be unrelated to what is happening around them. Most people with panic attacks experience several of the following symptoms:
Many factors are linked to the development of panic attacks and panic disorder. In terms of personality, those who are more prone to anxiety, and more likely to believe that anxiety is harmful, are more likely to experience panic attacks. Stressors and interpersonal issues, such as a death in the family or adverse life events, tend to be seen in the months preceding a panic attack.
Moreover, this hypocapnia and release of adrenaline during a panic attack cause vasoconstriction resulting in slightly less blood flow to the head which causes dizziness and lightheadedness.[28][29] A panic attack can cause blood sugar to be drawn away from the brain and toward the major muscles. Neuroimaging suggests heightened activity in the amygdala, thalamus, hypothalamus, and brainstem regions including the periaqueductal gray, parabrachial nucleus, and Locus coeruleus.[30] In particular, the amygdala has been suggested to have a critical role.[31] The combination of high arousal in the amygdala and brainstem along with decreased blood flow and blood sugar in the brain can lead to dramatically decreased activity in the prefrontal cortex region of the brain.[32] There is evidence that having an anxiety disorder increases the risk of cardiovascular disease (CVD).[33] Those affected also have a reduction in heart rate variability.[33]

Furthermore, certain organic diseases may present with anxiety or symptoms that mimic anxiety.[6][7] These disorders include certain endocrine diseases (hypo- and hyperthyroidism, hyperprolactinemia),[7][73] metabolic disorders (diabetes),[7][74][75] deficiency states (low levels of vitamin D, B2, B12, folic acid),[7] gastrointestinal diseases (celiac disease, non-celiac gluten sensitivity, inflammatory bowel disease),[76][77][78] heart diseases, blood diseases (anemia),[7] cerebral vascular accidents (transient ischemic attack, stroke),[7] and brain degenerative diseases (Parkinson's disease, dementia, multiple sclerosis, Huntington's disease), among others.[7][79][80][81]
Post-traumatic stress disorder -- or PTSD -- was considered to be a type of anxiety disorder in earlier versions of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders. But in 2013, PTSD was reclassified as its own condition. It describes a range of emotional reactions caused by exposure to either death or near-death circumstances (such as fires, floods, earthquakes, shootings, assault, automobile accidents, or wars) or to events that threaten one's own or another person's physical well-being. The traumatic event is re-experienced with fear of feelings of helplessness or horror and may appear in thoughts and dreams. Common behaviors include the following:
People with panic disorder often worry about when the next attack will happen and actively try to prevent future attacks by avoiding places, situations, or behaviors they associate with panic attacks. Worry about panic attacks, and the effort spent trying to avoid attacks, cause significant problems in various areas of the person’s life, including the development of agoraphobia (see below).