Your pain modifier represents penalties to Attack and Defence caused by your injuries, and provides modifiers as follows (colour-coded the same as the ‘pain mod’ rating in your score):
Current Health is at 75% or more of your maximum Health: No penalty. Your pain modifier will be coloured CYAN in your score.
Current Health is at 50% or more of your maximum Health: -10% Attack and Defence. Your pain modifier will be coloured BLUE in your score.
Current Health is at 25% or more of your maximum Health: -25% Attack and Defence. Your pain modifier will be coloured MAGENTA in your score.
Current Health is less than 25% of your maximum Health: -50% Attack and Defence. Your pain modifier will be coloured RED in your score.
Your pain modifier only affects Attack and Defence, but can still put you at a serious disadvantage. Note that certain talents or abilities may reduce or even completely negate pain penalties.