hi, thank you for providing the brief history of you. As mentioned you have undergone a TKR, post which due to infection another surgery was planned and the resting HR is high. So to understand this, the cardio respiratory endurance becomes weak as the immobility is prolonged. Also, undergoing physical therapy for the TKR is advised post TKR to ensure the mobility of the knee joint. while performing exercises, there will be an improved metabolism and immune system . Also, the improved metabolism, the digestive system will function to optimum post which your headache issue will be solved. Also, to understand that there is always a need for improved metabolism post any surgery as due to medications and immobility there is a lag in the digestive mechanism which needs correction. Also, in my personal clinical practice, I have Been dealing with the TKR cases and by implementing the regular early exercises helps them to early recovery and avoid additional health issues. Regards Jay Indravadan Patel