<unk>  is not preceded by any warning symptoms in approximately 50 percent of people. For individuals who do experience symptoms, the symptoms are usually nonspecific to the<unk> . This<unk> n present in the form of new or worsening: * chest pain * fatigue * blackouts * dizziness * shortness of breath * weakness * vomiting When<unk>  is suspected due to signs of unconsciousness or abnormal breathing, a bystander should attempt to feel a pulse for 10 seconds; if no pulse is felt, it should be assumed the victim is in<unk> . As a result of loss of cerebral perfusion (blood flow to the brain), the person will rapidly lose consciousness and<unk> n stop breathing. Near-death experiences are reported by 10 to 20 percent of people who survived<unk> , which demonstrates a certain level of cognitive processes that are still active during resuscitation.
Cardiac arrest
Respiratory arrest
Spinal shock
Syncope 
Permissive hypotension
Heat syncope
Sleep paralysis
Traumatic cardiac arrest