Panic attacks are periods of intense fear or apprehension of sudden onset accompanied by at least four or more bodily or cognitive symptoms like heart palpitations, dizziness, shortness of breath, or feelings of unreality and of variable duration from minutes to hours. Panic attacks usually begin abruptly, may reach a peak within 10 to 20 minutes, but may continue for hours in some cases. Panic attacks usually subside on their own over the next several hours. Often, those afflicted will experience significant anticipatory anxiety and limited symptom attacks in between attacks, in situations where attacks have previously occurred. The effects of a panic attack vary. Some, notably first-time sufferers, may call for emergency services. Many who experience a panic attack, mostly for the first time, fear they are having a heart attack or a nervous breakdown. Common psychological themes associated with panic attacks include the fears of impending death or loss of sanity; depersonalisation is relatively common.