Or, as Nicholas Sparks said, "When you're struggling with something, look at all the people around you and realize that every single person you see is struggling with something, and to them, it's just as hard as what you're going through."
If you don't know what to say to someone in chronic pain, don't worry. You don't have to say anything! Just be there and listen. No platitudes or advice; we just want you to treat us the same way you did before we became sick- as your friend.