Hypothetically Speaking: if one was to overdose & end up brain damaged would they care?

Again, hypothetically speaking: what if someone overdosed accidentally, of course, on sleeping pills and was rescued in time and lived but suffered the effects of brain damage. Would they know that something was wrong? Would they even care? Like would they really have the mental capacity to know that they were brain damaged? Or would they basically be like a walking vegetable floating around in some mental limbo?