how long can you hang upside down for?

[Penny]

me and my teacher were talking the other day and we got round to the question of how long you can be upside down for..

so..can anyone help me on this? I'd really like to know now :P

the question is - what is the absolute maximum amount of time a human being can hang upside down for? ..until the blood vessels burst or whatever happens.
and what would actually happen if you went past this time?

i've tried looking up but can't find it anywhere..would love to know

thanks

[Bmw-Rider]

until you fall off
get pushed off
get pulled off
loose your balance
loose your footing
loose your head for heights
loose all your money (from your pockets)