Also known as fainting, is a short loss of consciousness and muscle strength, characterized by a fast onset, short duration, and spontaneous recovery. It is due to a decrease in blood flow to the entire brain usually from low blood pressure.
Tunnel vision — your field of vision narrows so that you see only what's in front of you.
A cold, clammy sweat.
Complete blood count (CBC)
Potassium Sodium Chlorine (K, Na, Cl) (blood)
Transcranial duplex ultrasound of intracranial and extracranial vessels