Dilated pupils normally mean it's dark - and cats tend to be a little more lively in the night-time hours. The cat might be trying to get somebody to play with him or he might be hungry.

If the dilated pupils is a permanent thing - he is likely blind, which will affect his behavior. He is scared and will attack anything that comes near.

We have a cat that got West Nile a few years back - it made him blind (totally dilated pupils) and was really kind of crazy for a couple of years - we couldn't even pet him without him tearing into us. We persevered and he eventually learned to deal with his blindness. You often cannot tell when a cat is blind because they get so they know their surroundings so well that they can move around like nothing is wrong.