This effect only works on a PC when the PC is dying.
Dying means that the PC is at 0 or less hit points. ( HP <= 0 )
This effect creates a rate of HP loss while the PC is dying.
Death occurs when the death effect is applied. I don't remember if that is at -10 hit points or simply when you choose to apply a death effect.
This is an interesting effect and could be fun to play with in a death system.