If your Health is reduced to zero, then you have fallen unconscious and your turn ends immediately. Place your Health Marker on the zero space on your track and lay your miniature on its side in its current room to indicate it being unconscious.
On your next turn, you must perform a Rest Action to become conscious and stand your miniature up. After you Rest, you may move and then your turn is over. You cannot perform Free Actions if you started your turn unconscious.
Other heroes may perform healing spells or abilities to heal an unconscious hero; this immediately makes you conscious!