Octopus

We see another instance of very fast stormlight healing when Jasnah gets stabbed through the chest on the ship in from of Shallan. It is certainly possible that she soul cast a fake body to be stabbed. However, more likely she actually was stabbed, but because her brain and body can run on stormlight without oxygen a heart failure (or stabbing through the heart) is not death and can be healed just like any other injury– and that in fact Jasnah healed herself of even what would be a mortal wound quick enough to eslecall to shadesmar before the ship flooded.