Sinus infections often come with fever, reduced appetite, and mouth-breathing due to congestion. This combination can easily lead to dehydration. Low blood volume from dehydration causes blood pressure to drop, especially when you stand up quickly (orthostatic hypotension), leading to lightheadedness or a near-faint.
This is an excellent and important medical question. can sinus infection cause fainting
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 Sinus infections often come with fever, reduced appetite,