it isn't a brain tumor. there is zero evidence that it is such a thing. Lots of anxious folks jump to conclusions like that for no need.
yes, sinus or tension or stress, or any number of minor type things can cause it. sometimes sinus meds or ibuprofen can help this and sometimes not.
what would I do? if it was really bothering me, i would take meds mentioned above. if it didn't help, meh, I would shrug it off as just one of those weird things that happen in our bodies.