"How's your spiritual health?"
"It's fine. Why do ask?"
Answer a question with a question. The intent of their question isn't to get a straight answer, it's to put you ill at ease. Why would they ask that... they must know something... So, don't give them that opportunity. Put the pressure back on them. In essence you're saying, 'why would you ask that... what business is it of yours... are you insinuating something... they'll back off pretty quick