[Erik]

You should be looking where you're going if you don't know where the bottom is, no? I dive in terrible vis most of the time, and 'perfect' body position, equalisation etc is not usually an option. Don't stress about it in my opinion.
If I was just freediving, then I'd certainly be on a line. If I'm spearfishing (all I do anymore), then there's a line betwen the gun and the float at the surface. The vis we're in at a few lakes here means that at -15 metres it's so dark you can't tell up from down, so there must be some sort of reference line to the surface or it could mean death.