Why does it always happen in the middle of the night

Why do kids always get sick in the middle of the night? Friday I kept Camden home from school because he had a slight fever and a yucky cough. I took Addie to the doctor that afternoon with the same symptoms. All day I kept asking Camden if his ears hurt, of course he said no. Addie ended up with an ear infection. Saturday had more of the same....ran around playing all day, coughing with a slight fever, and always saying no his ears didn't hurt. Well around midnight a pitiful cry comes from the bottom of the stairs and works it's way up to our room becoming louder with each step...and low and behold I hear, "Mommy, my ear hurts" After some motrin and a back rub (if you know Camden this is his favorite thing in life, especially if you rub with your figernails and not your palm) he fell asleep. This morning he now complains of the other ear hurting also. Now do I take him to urgent care and pay out the nose, or do I wait until 6 pm when our doctor's after hours clinic is open and we pay $15...well since he is now intent on Nintendo again, I think I will save this weeks paycheck and wait until 6!