Have a plan
Treatments, appointments, medical bills, insurance claims, so many things add up over time. If you do not have a plan of action, you may accidentally let them collide in your schedule and cause you to freak out.
If you stay organized, establish a schedule, and fulfill tasks as they arise, then you can more easily stay on top of all of these events. Getting them out of the way expediently means that they will not loom over you and cause stress. Plus, if you follow your plan and knock tasks off with regularity, you may find yourself with more free time.
It will also give you a stronger sense of control over the situation.