Why am i almost passing out every time i stand up?

Dehydration?: This may be secondary to being volume depleted, or dehydrated. You may be taking medications that lower your blood pressure. Increase your intake of non-caffeinated beverages and see your doctor.

Anemia,orthostasis: Fainting episode or syncope can be caused multiple reasons the common ones are anemia , dehydration, arrhythmia, certain cardio vascular and neurological conditions. Simple test like hemoglobin and ekg can yield valuable information. Although syncope work up includes holter monitoring eeg and a ct scan or mri. Consult your physician asap.