Just sat for 20 minutes, eyes closed, and it was different.
After I'd settled, I got mental images, probably just the mind playing tricks. Iwasn't tired, like dozing off, but I was relaxed. I couldn't make out anything definite, just a lot of fuzzy images. I also felt nauseous at one point, and I also got the subtle feeling of spinning? I think at one point I also expereinced a slight pressure in my chest which disconcerted me for a brief while - but I son got back to the breath.
It was all in all though, an enjoyable expereince, different from open eyes meditation. Different in the ways described above.