1st you have to rehydrate your body with more fluids. 2nd you have to do cardiopulmonary endurance training e.g. cardio fitness with exercises on cycle/treadmill with progressions. You should go under supervision of Physiotherapist or Trainer who can concentrate n examine you also can calculate your stamina with your height weight and correlate it with your age too. That cardiovascular training is very important. Please Don't run on treadmill like a horse.It will affect your knee joints also. Regards-Dr.Gaurav Mohan from Physio Hut.