Why does Cyril says 'Mum what's the matter with you' ?

Cyril's surprise was because of her aberrant behaviour post the change of spirits with Mrs Fitzgerald. Mrs Pearson had said that dinner wasn't ready because she preferred to go out and get a square meal at Clarendon. She was in no mood to prepare dinner and that her children should fend for themselves. This took Cyril by surprise because his mother would never have said such a thing.