The two most common causes for syncope are neurocardiogenic (aka vasovagal) syncope and orthostatic syncope. Neurocardiogenic syncope is precipitated by certain situations such as blood-draws, hearing bad news, spraining an ankle, or playing the trumpet. Orthostatic syncope is triggered by moving from either laying to sitting or a sitting to standing position.
Other causes for transient spells of weakness or dizziness include hypoglycemia, migraines, seizures, and panic attacks. A less common cause is a cardiac dysrhythmia which can cause symptoms while the person is in any position.
Tests performed for evaluating syncope can include an EEG, EKG, provocative upper limb arterial duplex study for possible subclavian steal syndrome, and a 24-hr Holter-monitor. There could be further studies depending on the results of these initial tests.