You're probably familiar with the advice to drink plenty of water when you're sick. But one British woman recently ended up in the emergency room for following that advice with a little too much gusto when she had a urinary tract infection.According to a case study published in BMJ Case Reports , the 59-year-old returned to the hospital after getting antibiotics for her UTI because she was "increasingly feeling lightheaded and sick." She doesn't remember much of what happened after that, but her account in the case study sounds pretty scary."I remember seeing my hand in front of me shaking rather violently and I wondered why I could not stop it, then realized that my whole body was shaking," it reads. "At that point I became terrified and am told that on three occasions I said I was 'turning into my mother.'" She left the hospital after a day and took a full week to recover.The doctors diagnosed her with acute hyponatremia, which involves plummeting sodium levels that may cause brain swelling, a coma, or even death, according to the Mayo Clinic . It can have a variety of symptoms, including nausea, vomiting, and headaches.The study also mentions another case of a woman who developed acute hyponatremia after drinking too much water while suffering from gastroenteritis. "Together, these two cases highlight…the need to qualify our advice regarding water consumption in simple infective illness," it reads.Dr. Maryann Noronha, one of the UTI sufferer's doctors, told Live Science that drinking too much water can decrease sodium levels in the blood, which means "water will be pulled out of your blood vessels into areas that are more concentrated, as the body tries to balance things out again." This can lead water to fill up the brain, which causes the swelling.Hospitals can detect hyponatremia with a blood test, but they don't always know to look for it, since its symptoms can be associated with so many other illnesses. If the cause of your suffering truly is drinking too much water, it should get better once you drink less — in this woman's case, a liter over the course of the day.To hydrate without going overboard, the smartest way to go is to listen to your body's cues — if you're thirsty, drink (the old "eight glasses a day" rule is handy and easy to follow, of course, but it's not really based on evidence). You might need a little more when you're sick, but obviously, there's a limit.