Many different conditions can cause fainting. These include heart problems such as irregular heart beats, seizures, low blood sugar (hypoglycemia), anemia (a deficiency in healthy oxygen carrying cells), and problems with how the nervous system (the body's system of nerves) regulates blood pressure.

Why do I feel faint or weak?

Causes of lightheadedness may be dehydration, medication side effects, sudden blood pressure drops, low blood sugar, and heart disease or stroke. Feeling woozy, lightheaded, or a little faint is a common complaint among older adults.

What are you lacking if you feel faint?

Dizziness

Frequent bouts about dizziness and vertigo can indicate B12 deficiency. You may experience a feeling of wobbles when you get up too fast from a sitting position.