They're called "never events," the medical errors we hope never occur, like operating on the wrong patient or leaving a sponge behind after surgery. Nevertheless, they do happen about 4,000 times a year. But they're not really what you should be worrying about.
HHS has just released a study verifying that one fourth of Medicare patients are harmed while being hospitalized. Those medical errors are called "hospital acquired conditions" and almost half are preventable. Falls, infections, misdiagnoses, faulty medicating. All result in patients who now have a medical ailment they didn't have when they were admitted. Many do not survive to be discharged or are permanently impaired.
Please consider how you can be a more engaged--and safe--patient. Then start making self-advocacy a priority in your own health care journey.