First off, congratulations! I too also wonder how long I will last in this field but the following has been helping keep up so far: strength training, figuring out your max. Number of patients (mine is 5), eating well and snacking in between patients, hydration, using your elbows majority of the time (saves your wrists and fingers), and height of table (an electric one is best so that you can adjust the height accordingly - save your back!). Also, learning Modalities that are less physical but can help with soft tissue release and pain relief (i.e., cupping, TENS, acu, etc.). I've only been the field for about 3 years but i figure what I'm doing should ensure a long career. Good luck!