AFAIK there is no overall screen effect when toon gets a damage. I can only see a red number, sometimes a big red number, sometimes it has orange color (in epic quests). I suggest to add some graphical effect like in other games when player is hit. Especially when he is hit for large damage or his HP bar is low. It can be just some red (blood) border around the scene.
If there is already some option to turn on this feature, tell me please where. Getting damage generates a pain and I wish to feel the suffering of my toon.