How Do I Tell People I Have an Auto-immune Disease?

Is there any right time to tell someone about your autoimmune disease? This is one of the hardest parts about living with a disease that only flares every so often. It's important that people are aware of what I have, but it's hard to know when exactly to tell someone. I want people to know about it but if I talk about it to someone, I don't want them to think I am trying to get them to pity me for it or something. There's just a comfort in knowing that the people around you are somewhat aware of it.

It was really hard for me to tell people about what was going on with me in 11th grade. People would write on my Facebook wall asking me how I was feeling and when I was coming back to school and I never knew what exactly to reply. I wanted to express how I was feeling in a much deeper way than Facebook would enable me to. I didn't want to post all my health information in public, but I even felt uncomfortable sending private messages. How can anyone ever know what exactly you are trying to say over a message? If I type a message to someone on Facebook and say, "I got a spinal tap today, an IV, and now I'm feeling worse than ever", it may sound like I am feeling bad for myself. It also didn't really help me much when I typed out a response to someone's question about how I was feeling. In order to feel any different after, I needed to actually verbally speak to them. I felt more comfortable doing this, and it actually had positive affects on my mood.