The "supernaturalism" started to get to me after a while. Like speaking in tongues, when I found it increasingly plausible that they were all (those with "the gift of tongues") basically faking it without knowing that's what they were doing, "miraculous" healings for things that tend to heal themselves, but no miracles for more serious stuff that doesn't ever normally self-heal, a few traveling "apostles" who struck me as full-on scam artists, realizing that some of my spiritual experiences were just epileptic seizures (I was diagnosed with epilepsy)...stuff like that.
It's hard to be filled with the spirit when you're battling cognitive dissonance, and I think the part of your brain that can do "faith," and the part of your brain that can do a universal sort of critical thinking are in diametric opposition.
My faith just sort of slowly evaporated over time, and I'd pray passionately and frequently for my faith's return, to no avail. Going to church became depressing.
And then one day as I was sitting there praying, I realized that quite possibly I was attempting to communicate with air above the ceiling, and how preposterous that activity was, if it was true that there was nothing out there hearing my prayers. I allowed myself to truly explore the idea of if maybe the whole thing had always been just in my head and in everyone else's head. I realized I'd been brainwashed into Christianity as a kid, and that I'd always taken god's existence as basically axiomatic.
I decided that if a good and benevolent god existed, He would be fine with me just sort of starting over on the religion question and looking for Him from the perspective of an agnostic/atheist.