For me personal, pulminary hemorrhaging was the worst. When you're lungs are due to collapse and you end up in ICU is definitely a scary thing. Any blood loss is so dangerous to the haemoglobin levels of a GPS sufferer. Just maintaining a low, but acceptable level of Haemoglobin can be changing or several cycles of blood transfusions would needed. Water retention is also a factor while needs to monitored strictly. In my case, too much weight gain and water retention led to relapse of GPS