The difference between the OP's and your mother's situation is that OP got injured after becoming an adult. The real difference is that OP could could determin

The difference between the OP's and your mother's situation is that OP got injured after becoming an adult. The real difference is that OP could could determine if his current state is a regression from normal. Your mother's abilities degraded before she could understand what she misses out on. So being disabled is the norm for her, she does not feel disabled, but when filling out official forms, she has to compare her abilities with her perception of "normal". So it's not that OP is wrong, he is just in a different situation, they are both right.