Even though you say you are laying on the floor, I do believe those areas receive more sunlight. Shoulders in particular can be hit by sunrays whether you are lying on your back or on your stomach. Additionally, it might not be much, but any time you spend standing makes the shoulders receive much of the light directly.

Sure mate, you go ahead an keep believing that the reason you’re not as good as Mozart is because you weren’t given the tools… Otherwise!!