I actually did that (or something similar) last week. My son has been hospitalized a few times. He is 4. He has been poked, prodded, allergy tested, iv'd, etc. until the poor kid probably feels like a science project. He had his well child visit that was WAY overdue, because honestly we are in there so much that I can't keep up with it all (plus I have 2 more kids). He is due for shots between 4yo and 6. I didn't ask him if he wanted the shots, but I decided to wait because I like to tell him in advance what is going to happen so we can be prepared. A little less hassle for whoever has to administer.
Also, a few weeks back my youngest had been sick all week. Dr on Mon. ER on Fri...turned out he had strep. Maybe he had it Monday, don't know - wasn't tested, doesn't matter. Because aforementioned child is sick alot, called dr same day appt to have him tested to be on the safe side. Truck overheated before I could even get out of town (I live 45 minutes away from dr). Hated to do it, but had to cancel. Dr's office very forgiving thankfully.
These things really do happen.