Sinusitus can make me incredibly mentally dull like you would not believe. I've have had covid years ago and that is the closest comparison I have for mental effects and tiredness.
For me sinusitus starts out as a minor odd feeling in the throat progressing to increasing sensitivity to noise and then the mental effects. I've had it maybe four times in six years. The first time was the worst with all the classic severe symptoms - full on forehead headaches all that stuff. I'm recognizing it earlier each time so the severe classic symptoms are not a problem this time. Antibiotics make me feel terrible so I'm going to avoid those if I can get some symptom relief from other means.
What works for you?