Occasionally when I've been astral, but still in my physical body, I've been able to roll my astral body around 180 degrees and experienced being face down (astrally) and face up (physically) at the same time, in the same space. Quite bizarre and memorable.
I've not done the feet up in the air acrobatics - but I believe quite a few have - if I remember rightly, Nay had a spell of getting her whole body out except her head which meant that she was literally upside down vertically... Nay?
Oh, that reminds me, I have also walked upside down on the ceiling. That was pretty strange and wonderful too.
Sarah