This is a weird one so let me explain.
Sanity's eclipse refers basically to the (temporary) loss of one's sanity. Delusion's horizon is the funny part though. There are two times when you can see the horizon, sunrise and sunset.
In other words, we need some delusions. Those are the delusions that keep us going despite the shit that happens to convince us to give up. But take it too far, and we're consumed by it.
Same old lesson that we should all know, I just wanted to make it 5 words long (and idiosyncratically esoteric), so that I could remember it better.