Once, in my very early days of mastering, I edited for 8 hours straight, on a weekend, probably a sunny one. It was a massive project that needed a lot of detail work, and, as the assistant, that was my job. When I left work, I couldn't focus my eyes because I'd been staring at Sonic Solutions for so long. I had a moment of panic: this is it, I've half-blinded myself. My eyes recovered in a few hours, and I haven't run any editing marathons like that since. I wised up and learned to take breaks. This morning, somewhat randomly, I listened to a song from that album (which shall remain anonymous). And you know what? It sounded great!
And you know what else? I still love editing.