Oh it's nothing formal, I just try to avoid any stress to my spine. That is, I don't sleep in strange positions that I used to sleep and I changed my bed to a stiffer one because the old one was deforming too much by my weight and this was causing my sleeping position to be slightly curved.

I also looked around the internet for recommendations but they all converge the idea that you shouldn't be forcing your spine to stay in a curved position beyond the natural curve for too long.