When your brain doesn’t get enough oxygen, you may experience lightheadedness and weakness, as if you’re going to faint. If you don’t, that’s a presyncope. If you do faint, that’s called syncope.

If you’ve ever felt dizzy, lightheaded, or like you were about to faint, but you didn’t lose consciousness, you may have experienced presyncope. It can be caused by many conditions, including heart ...