If we're to be blatantly honest, we have no idea. There are theories ranging from the Flood to rogue AI messing with his brain. Personally, I see way too many problems with the Flood theory for it to be possible, but the rogue AI theory makes some degree of sense. If I were you, I'd take every theory with a massive grain of salt. Listen to them, but don't buy into any of them. As for FERO, same deal. Tons of theories, no definitive answers. We can at least discount Halsey, as it doesn't sound anything like her.