What happens if a kalashtar becomes possessed?

Kalashtar have Quori spirits inside of them. How would the spirit react to being possessed. If there are no game mechanics that could be added, could any flavor be added to spice up the campaign in the event of a possessed kalashtar? Eberron: Rising from the Last War says that there can be adverse effects if a kalashtar ends up being an evil alignment, would this apply to being possessed by an evil PC?