Sometimes (OK, more than sometimes), our health system is a bit crazy.
Hospitals will sometimes put you on observation status rather than admit you. Of course, there is a reason they do that, and it isn't to help you out. They do it to keep their readmission rates down, which can cost them money. So, to save money, they put you at risk of having to pay more.
You can be there for days, have multiple tests and exams and still be on "observation status".
The best thing you can do, is to check on the admission status and argue to get it changed while the patient is first admitted to the hospital.
After they are out, there is no appeals process and you are stuck.
On Observation Status, you can have higher costs for insurance and drugs. However, the real problem comes if you need to go into a nursing home. If you were admitted to a hospital for 3 consecutive days, you get Medicare coverage for 100 days for a nursing home.
If you were on observation status for 3 days, you pay the cost for 100 days. At $12K a month, that can be close to $40K in Fairfield County Connecticut or Westchester County New York.
There is a great New York Times article on the latest news.