I would definitely discuss with it his GP - if he is of a good weight not eating for a day or two may be OK but not drinking will have bad consequences very quickly and it will only add to his distress and cause confusion/headaches/falls.
As Grannie G said the GP may be able to prescribe something to lessen his distress and also, if thought necessary, prescribe some food supplement drinks (Ensure for instance) that are very high in calories to compensate if someone has a poor food intake - although the not drinking would still have to be addressed too.
Good luck.