When Richard is a little boy, his mother suddenly gets sick. She never really gets better, and a lot of the time she actually gets worse. We don’t know why she gets sick, and no one ever seems to have a very good explanation.
Mrs. Wright’s inexplicable, constant illness comes to symbolize suffering. Richard lays it out for us: "My mother’s suffering grew into a symbol in my mind, gathering to itself all the poverty, the ignorance, the helplessness; the painful, baffling, hunger-ridden days and hours; the restless moving, the futile seeking, the uncertainty, the fear, the dread; the meaningless pain and the endless suffering" (1.3.324).
So, not only does she have to suffer through being sick all the time, she has to bear the burden of representing Richard’s suffering, the suffering of black Americans, and the suffering of all oppressed people everywhere. That’s a heavy burden to lay on a sick lady, Richard.