"Right" and "Left" and "Top" and "Bottom"

If you are lying down, "above" and "below" continue to be with respect to gravity.

Hence, when you're lying down, the ground is below you, and the sky is above you.

You might refer to things "at your feet" or "behind your head".

To my right there's a wall, to my left there's a desk, above me there's a ceiling and below me there's a floor.

'Top' and 'bottom' are not directions (or prepositions), they are features of a static object by itself: 'the top of my head'.

'To my top' sounds like a direction but is somewhat infelicitous; it sounds like you are a box. You'd prefer to say 'towards my top' or 'towards my head' and that can come from any direction around the top/head.

'Above' and 'below' are the directions (and grammatically prepositions). They go in the direction according to gravity. If you are hanging upside-down, 'above you' is in the direction of your feet.

If you are on the space station with no gravity, it is relative to your head, 'above you' is always in the direction out the top of your head. But that is not particularly common usage. 'above you' is by far away from the pull of gravity.

If you are lying on the floor on or near Earth's surface on your back, I would take above you to mean above your ventral surface; that is, away from Earth's center, along a radius, out toward space.

Along the head-to-foot axis, or anteroposterior axis, "the polar opposite to the anterior end is the posterior end", your head being at the anterior end of your body, according to vertebrate directional terms in wikipedia.

The terms top and bottom are used ambiguously in your question, as top might refer to any of dorsal, ventral, or anterior, depending on whether you regard top as equal to spatial direction up, vs taking it as a body-relative term.

These questions (and many others) are answered in Fillmore's Santa Cruz Deixis Lectures. The one to read about these terms is Lecture 2, entitled simply "Space".

Since Fillmore is a far better writer, I forbear to summarize them here. Go the source.