We're physically geared to deal with emergencies as they happen, fall apart afterwards, when it is "safe".

Too, sometimes it can take a while for a condition/event to matter, for all its ramifications to be understood; at first we can just be kind of stunned or not see the whole picture. If the brain is use to things being a certain way, it will take it awhile to realize they are not like that anymore to "see" things differently than they expect to. That could be why we catch sight of a loved one who may have died, after they have died; the brain is still getting use to the loss, has residual connections.