FullyFlapped, Ronny3585 is *wrong*. At least, in the UK, the following applies:
"No aerobatic manoeuvre may be flown over the congested area of any city, town or settlement. Aerobatics may only be carried out in controlled airspace with the permission of the appropriate ATC unit. 'Aerobatic manoeuvres' include spins, loops, rolls, stall turns, inverted flight and similar manoeuvres."
That's in addition to rule 5. And common sense obviously dictates a minimum height far above the rule 5 heights.
The military,
AFAIK, uses 3000 feet as minimum height. If you get below that and have not recovered your manoeuvre, you bail out and get a new airplane. That last bit may be a bit extreme for a private pilot, but using 3000 feet as your minimum height anyway makes sense. If any manoeuvre ends up below that height, declare "game over". Stop your routine and go home.