Because by walking into the hospital, you already gave away the info to any bystander. And all variations thereof.
If you're coming in for a disembowlement, sure, but even then you're only really revealing the condition; your name, history, insurance details etc. are still private information. (The hospital would also still be forbidden from, say, publishing "amelius came in today with with a minor disembowlement" without your permission, no matter how public it was in the waiting room.)
Btw, my name's not Geoff.
(Just to be a bit more plain.)