Don't worry about sleeping with the flush. As long as you're lying there not moving too much that's fine. I doubt that many of us can fall asleep at 10pm.
The very first time I used the zapper I became incredibly thirsty, so I felt like something was happening. Since then, nothing. I don't really know what they're all about but I don't think it's something I've really needed. Like all of these "cures", though, there are people who swear by it. Who knows?