Panic attacks are periods of intense fear or apprehension of sudden onset accompanied by at least four or more bodily or cognitive symptoms (such as heart palpitations, dizziness, shortness of breath, or feelings of unreality) and of variable duration from minutes to hours. Panic attacks usually begin abruptly and may reach a peak within 10 to 20 minutes but may continue for hours in some cases. Panic attacks are not dangerous and should not cause any physical harm.