My Son Needs A Nap

My son is 28 months old now and he takes a nap once a day for at least two hours. He naps around 1pm to 3pm. Sometimes he'll miss a nap or two during the week especially when we're out for an appointment that will last beyond his nap time or at the same time as his nap time. But I make it a point that he won't miss it for two consecutive days, otherwise he'll be miserable and so am I. Nap time to my son is really important, otherwise he gets increasingly tired, whiny, and miserable. I read that if a child is overtired, his body no longer responds as well to his brain signals, so he becomes less and less physically coordinated and more and more frustrated. I always say that my son is 'out of tune' if he doesn't get a nap, exactly what happened yesterday. We had dinner party at my girlfriend's house at 2pm and my son didn't take a nap. He was overly active playing with his playmates at the party too. So at around 6:30pm he became whiny and uncoordinated. Then at bedtime he was restless and cried at least three times. I had to go in his room to calm him down once. No more missing naptime for my son.