A panic attack can result when up-regulation by the sympathetic nervous system (SNS) is not moderated by the parasympathetic nervous system (PNS). The most common symptoms include trembling, dyspnea (shortness of breath), heart palpitations, chest pain (or chest tightness), hot flashes, cold flashes, burning sensations (particularly in the facial or neck area), sweating, nausea, dizziness (or slight vertigo), light-headedness, heavy-headedness, hyperventilation, paresthesias (tingling sensations), sensations of choking or smothering, difficulty moving, depersonalization and/or derealization. These physical symptoms are interpreted with alarm in people prone to panic attacks. This results in increased anxiety and forms a positive feedback loop.