I missed out a question on a English GCSE?

Recently, I did English Paper 2 higher tier and I accidently missed out section B, is there a way I can redo it before it gets marked? I has a middle B in my English mock, how will this bring me down? My coursework is a B as well. The reason I accidently missed out Section B was because I have chronic disequalibarium so I feel dizzy/unbalanced when I sit still, and when it happens, I go nervous and start shaking so I can't concentrate properly. Is there anything I can do? I usually get B's in English. Is it worth informing my school?