Heat cramps
Heat edema
Heat exhaustion
Heat tetany
Heat stroke<unk> 
Miliaria
Hyperthermia
Cardiovascular-mediated<unk> 
Dysrhythmias:
WPW (pre-excitation)
Long QT Syndrome/QT prolongation
Brugada Syndrome
Catecholaminergic polymorphic ventricular tachycardia
2nd/3rd AV Block
Afib/aflutter
Vtach/torsades
Sick sinus syndrome
Arrhythmogenic right ventricular dysplasia
Short QT syndrome
Cardiovascular disease
Valvular Disease (AS, MS, tricuspid stenosis)
Aortic Dissection
Myocardial Infarction
CHF
Hypertrophic Cardiomyopathy
PE
Pericardial Tamponade
Myxoma
Pulmonary Hypertension
Pacemaker malfunction
Neurally mediated<unk> 
Vasovagal:
Fear, pain, emotion, valsalva, breath-holding spell
Situational (associated with):
Coughing, micturition, defecation, vomiting, swallowing, postexercise
Carotid sinus stimulation
Orthostatic hypotension-mediated<unk> :
Volume depletion:
Dehydration (vomiting, diarrhea)
Hemorrhage, (Ectopic Pregnancy, Upper GI Bleed/Lower GI Bleeding, Abdominal Aortic Aneurysm)
Sepsis
Autonomic Dysreflexia
Autonomic failure due to meds
Other serious causes
Stroke
SAH
TIA
Vertebrobasilar Insufficiency
Subclavian steal<unk> 
Hypoglycemia
Hyperventilation
Asphyxiation
Seizure
Narcolepsy
Psychogenic (anxiety, conversion disorder, somatic symptom disorder)
Toxic (drugs, carbon monoxide, etc.)
Dysrhythmias:
WPW (pre-excitation)
Long QT Syndrome/QT prolongation
Brugada Syndrome
Catecholaminergic polymorphic ventricular tachycardia
2nd/3rd AV Block
Afib/aflutter
Vtach/torsades
Sick sinus syndrome
Arrhythmogenic right ventricular dysplasia
Short QT syndrome
Cardiovascular disease
Valvular Disease (AS, MS, tricuspid stenosis)
Aortic Dissection
Myocardial Infarction
CHF
Hypertrophic Cardiomyopathy
PE
Pericardial Tamponade
Myxoma
Pulmonary Hypertension
Pacemaker malfunction
WPW (pre-excitation)
Long QT Syndrome/QT prolongation
Brugada Syndrome
Catecholaminergic polymorphic ventricular tachycardia
2nd/3rd AV Block
Afib/aflutter
Vtach/torsades
Sick sinus syndrome
Arrhythmogenic right ventricular dysplasia
Short QT syndrome
Valvular Disease (AS, MS, tricuspid stenosis)
Aortic Dissection
Myocardial Infarction
CHF
Hypertrophic Cardiomyopathy
PE
Pericardial Tamponade
Myxoma
Pulmonary Hypertension
Pacemaker malfunction
Vasovagal:
Fear, pain, emotion, valsalva, breath-holding spell
Situational (associated with):
Coughing, micturition, defecation, vomiting, swallowing, postexercise
Carotid sinus stimulation
Fear, pain, emotion, valsalva, breath-holding spell
Coughing, micturition, defecation, vomiting, swallowing, postexercise
Carotid sinus stimulation
Volume depletion:
Dehydration (vomiting, diarrhea)
Hemorrhage, (Ectopic Pregnancy, Upper GI Bleed/Lower GI Bleeding, Abdominal Aortic Aneurysm)
Sepsis
Autonomic Dysreflexia
Autonomic failure due to meds
Dehydration (vomiting, diarrhea)
Hemorrhage, (Ectopic Pregnancy, Upper GI Bleed/Lower GI Bleeding, Abdominal Aortic Aneurysm)
Sepsis
Stroke
SAH
TIA
Vertebrobasilar Insufficiency
Subclavian steal<unk> 
Hypoglycemia
Hyperventilation
Asphyxiation
Seizure
Narcolepsy
Psychogenic (anxiety, conversion disorder, somatic symptom disorder)
Toxic (drugs, carbon monoxide, etc.)
Heat syncope
Heat cramps
Panic attack
Heat edema
Heat stroke
Heat exhaustion
Electrical storm
Heat tetany