In retrospect, my mother's troubles may have begun with a urinary tract infection; older women are especially prone to UTIs without the usual symptoms. Or maybe her abdominal pain was unrelated, and she contracted sepsis from an IV line in the hospital. Whatever its source, no one thought of sepsis until the evening, when my mother's lungs stopped working. Though the doctor administered antibiotics right away, her kidneys failed several days later. Soon afterward, she died.

"Distinguishing sepsis from the original infection is not easy even for a seasoned clinician, because the symptoms can be very similar," says Steven Opal, MD, a professor of medicine in the division of infectious diseases at Brown University's Alpert Medical School, and chair of the International Sepsis Forum. "It's often the family that sees something is just not right. They see that the patient is not behaving the way she usually does."

In fact, my father noticed my mother's confusion in the hospital, but he had no idea it could be a symptom of sepsis, or what sepsis even was. If he had, he might have been able to flag it for doctors, who didn't know my mother's usual mental state.

Other signs to watch for include feeling disproportionately ill (for instance, if a skin infection leads to loss of appetite or extreme dizziness) and getting worse rather than better while being treated for an infection. If that happens while you're home, says Opal, go back to the doctor sooner rather than later: "People wait too long. They don't realize how fast things can happen."

Maybe my mother would have lived if she had been put on antibiotics sooner. Maybe not. All I know is that we would have had a better chance at a happy ending if any of us—doctors, friends, family members—had been watching for the signs.

Harriet Brown is the author of Brave Girl Eating (William Morrow), a memoir of her daughter's battle with anorexia.

Next: The 7 warning signs of sepsis