You have a character who is dying or has a disease/condition that puts their life at risk. Maybe cancer, ALS, or even just getting on in years. Whatever the reason, they may have decided they don’t want life-saving measures performed if they get worse. This could include CPR, defibrillation, intubation, feeding tubes, IVs, certain medications, etc. Or maybe, your character is the nurse/doctor caring for this patient. How does the healthcare team treat patients who are DNR (do not resuscitate)?
Your character got a bad knock on the head; happens to the best of us. Although tempting to write the following scenario, DON’T! Your character is punched. They’re unconscious for several minutes before waking up with a headache, maybe a bit out of it/acting silly. A week later (or worse, later that day), they are back to their plucky selves, fighting crime, getting into mischief, what have you.* Unfortunately, if you’re going for a realistic story, that ain’t happening.