Whatever happened to Claire happened to Sayid. It has something to do with the Magic Hot Tub being contaminated when they were dunked. Claire was taken there at some point, and that's when she turned cuckoo evil crazy. Perhaps when the water is not clear, it increases the chances of the healed person being infected by evil? Like, when the water is clear, it's the Jacob Forces doing the healing, but when it's murky it means there's some MIB in there too?

Claire went full-on Rousseau-paranoid. Sayid hasn't had a chance to get there, I think.