Hi My Elderly Cat,16 Has Been Hiding Today And I

Hi my elderly cat,16 has been hiding today and I realized that he hadn't eaten today. His pupils seem larger than normal and I don't think that he moved all day. When we offered him a can of food he ate some of it,and acted pretty normal,purring etc. His pupils contracted some when we shined a light in his eyes,but not as much as normal. My question is does he need to go to the emergency vet or can it wait until morning?