You will need a doctor's note. When you get your "packet" from the Court it will explain what you can do (reschedule, change location, etc) and what is needed to be excused (doctor's note). Good luck!
Call the people who summoned you for the answer to your question, because they get calls all day long from people who want out. I have bad hearing and called them about that, and they agreed that I don't have to go for my summons which happens to be next month.