Vertebro-basilar arterial disease
Arterial disease in the upper spinal cord, or lower brain that causes syncope if there is a reduction in blood supply. This may occur with extending the neck or with use of medications to lower blood pressure. Other causes
There are other conditions which may cause or resemble syncope. Seizures and syncope can be difficult to differentiate. Both often present as sudden loss of consciousness and convulsive movements may be present or absent in either. Movements in syncope are typically brief and more irregular than seizures. Akinetic seizures can present with sudden loss of postural tone without associated tonic-clonic movements. Absence of a long post-ictal state is indicative of syncope rather than an akinetic seizure. Subarachnoid hemorrhage may result in syncope. Often this is in combination with sudden, severe headache. It may occur as a result of a ruptured aneurysm or head trauma.Heat syncope occurs when heat exposure causes decreased blood volume and peripheral vasodilatation. Position changes, especially during vigorous exercise in the heat, may lead to decreased blood flow to the brain. Closely related to other causes of syncope related to hypotension (low blood pressure) such as orthostatic syncope. Lactose intolerance can cause "a release of histamine, resulting in an extreme dilatation of the bloodvessels, resulting in a drop of blood pressure so that not enough blood reaches the brains, leading to dizziness, fainting, syncope, itching, hives, tingling or swelling of the lips, tongue, or throat; chest tightness, shortness of breath, or difficulty breathing, wheezing." (More in the article on 
 Lactose intolerance).
Other causes of similar symptoms that should be considered include seizure, stroke, concussion, low blood oxygen, low blood sugar, drug intoxication and some psychiatric disorders among others. Treatment depends on the underlying cause. Those who are considered at high risk following investigation may be admitted to hospital for further monitoring of the heart.A hemoglobin count may indicate anemia or blood loss. However, this has been useful in only about 5% of people evaluated for fainting. The tilt table test is performed to elicit orthostatic syncope secondary to autonomic dysfunction (neurogenic). A number of factors make a heart related cause more likely including age over 35, prior atrial fibrillation, and turning blue during the event. Electrocardiogram
Electrocardiogram (ECG) finds that should be looked for include signs of heart ischemia, arrhythmias, atrioventricular blocks, a long QT, a short PR, Brugada syndrome, signs of hypertrophic obstructive cardiomyopathy (HOCM), and signs of arrhythmogenic right ventricular dysplasia (ARVD/C). Signs of HCM include large voltages in the precordial leads, repolarization abnormalities, and a wide QRS with a slurred upstroke. Signs of ARVD/C include T wave inversion and epsilon waves in lead V1 to V3.It is estimated that from 20 to 50% of people have an abnormal ECG. However, while an ECG may identify conditions such as atrial fibrillation, heart block, or a new or old heart attack, it typically does not provide a definite diagnosis for the underlying cause for fainting. Sometimes, a Holter monitor may be used.