Sepsis is a disease that kills more people than breast, lung and prostate cancer combined, and causes one million hospitalizations every year. Never heard of it? You're not alone; seventy-five percent of the population is not familiar with this killer. "Sepsis is a toxic response to an infection," explains Dr. Jim O'Brien, a director at the Sepsis Alliance. "Your body has an entire army in it that is built to beat infections, which is great when it's shooting bullets and hitting bacterias and viruses. The problem with sepsis is that your body basically suffers friendly fire, and as a result, instead of protecting you, your body winds up starting to kill you." Dr. O'Brien outlines some of the symptoms that people should be aware of. "If you're feeling very short of breath or light headed or confused," he says. "And the other phrases we hear patients tell us is, 'This was the worst I ever felt,' or, 'The most severe I ever had.' Those are the times to start being worried that this is more than a cold, that this is something that you need to seek help for." Watch the video above to hear from Dr. Carl Flatley, and how the death of his daughter Erin from sepsis prompted him to begin the Sepsis Alliance to bring awareness to the disease. "Even if you can't explain what sepsis is," he says, "when you go into the hospital for absolutely anything, you tell everyone there, the nurses and doctors, that you're concerned about sepsis. That puts them on notice that you know something about it, and that makes them take that extra step to heighten their awareness about it."