zebra finch sneezing — when should I worry?

My Pionus has been sneezing a few times a day for the past week. No discharge, still eating and playing normally. Could it be the dry winter air from heating? Or should I book a vet visit?

Did this start suddenly or was it gradual? When my lineolated parakeet did this it turned out to be jealousy of a new person, pet, or even object in the home.