The feeling of faintness during a sinus infection is usually tied to how the infection impacts your balance systems: How Sinus Can Cause Dizziness | ENT of Georgia South
Your sinuses are very close to your Eustachian tubes and inner ear. Severe congestion and inflammation can spread or cause dysfunction in the vestibular system. This leads to vertigo (a spinning sensation) and significant imbalance, which can feel very much like you are about to pass out, even though you aren't. can sinus infection cause fainting