This is the official medical term for fainting or sudden loss of consciousness. “Pre-syncope” is the feeling that you’re about to faint.
The most common form is “vasovagal syncope” which means you have a sudden drop in blood pressure which causes you to faint due to lack of oxygen to the brain, so-named because the vagus nerve regulates heart rate (among other things).
It’s pronounced “SINK-o-pee.”