So I started walking every day more than one month ago and my post exertional malaise seems to have improved in distance. I have got to walk up to 12 km (7.5 miles) at very high speed (6.5 km/h) and I didn't get the dreadful malaise. However, this is just for walking. The other day I went to throw the basketball, just some throws without really running or playing, just some jumping and some short runs to the basket, and after around 30 minutes I got the symptoms so bad that I had to go to Emergencies (electrocardiogram ok) with all the same symptoms I've had for 25 years when exercising... feeling of heart angina, can't breath, nausea, dizziness, flu-like feeling, pallor, ... And today it happened again when I went to the gym to exercise my muscles. Indeed I have improved after one month walking and some short trainings at the gym, but went a bit far and again the symptoms are there. And it is very scary because it really feels like heart disease, angina, like I'm going to die for many many hours or even days. So, my doubt is if it gets any better if I keep training but stop when I am forcing the muscles and start feeling the symptoms. My feeling is that it can improve a little bit, but still the muscles and aerobic exercise is impossible it's a gone function in my body for anything that means a bit heavy muscle use and oxygen demand.