Player down play continues!

I believe it is somewhere in the Rule but not sure. However, I've always been told and done things this way. If player is severly injured blow it dead right away. I would consider being knocked out severe. If player is in danger of being injured further or another player is in danger of being injured because of location of first injured player, blow it dead. If injured player is out of harms way wait until play has stopped then blow it dead.