One thing that is common in many first person games is screen damage, it helps to immerse the player into their current state. To save time I purchased a pack that would replicate the feature for me however I still had to implement it and fix it to work with the health system I had up to that point. This meant understanding how it worked and cross linking the current health and damage variables.
Upon reaching low health the screen blood will begin to pulse and a heartbeat sound begins to play, this is to heighten the feeling of fear and intensity of the players stituation.
Why use screen damage?
As discussed in this blog post by Jasper Stephenson who discusses' the benefits of using screen damage in first-person games, first and foremost, he comments on how it is a very straight forward and universally understood way of showing "You Got Hit" "Danger". Furthermore as mentioned at the start it also really does help immerse the player and allows them to judge their current success in a fight without just having to stare at a health bar.
Thanks for Reading!