Why do we go to the doctor?

I have been pondering this as by kids have been sick with the croupy hacking cough. Normally they get the colds but the hacking cough is a first. They have been sick. I know it. But why is it that the instant you take them to the doctor they are immediately all better. But only for the visit right. They bounce off the walls and are as happy as can be. Their fevers magically disappear. I know my doctor must think, "well gee they seem fine to me, take em home" And then once you get home, the cough starts again and the fussing too. You feel like a bad parent cause you hadn't taken them cause you think oh.. they'll be better in a day and then afterwards you feel like oh ... I could have waited... its just a cold right. Maybe someone can explain this to me, I am at a loss... its as if they are secretly conspiraring againgst me.