I used to guard against it but I have basically stopped that. I am tired of hiding. I don't care if I am excluded or whatever...don't really think that has happened.
I don't (as other posters have mentioned) tell everyone I meet. But when someone becomes my friend I casually work in into the conversation.
My behavior can be very erratic when I am sick. I think telling friends has helped them understand things. It is much easier for me to go along and do things if they know I get tired easily, etc.
When I am depressed i don't feel like moving. If friends didn't know, they would think I didn't like them or were ignoring them.
The ONLY place I never told anyone was work. It is none of their business.