If you have an invisible disability, or any disability at all I suppose, you should have your spiel down. You need a little 20 second explanation that both reassures the listener you know what you’re talking about and are on it, and it’s serious and they shouldn’t brush it off.
Me: “I’ll take the elevator.”
Not me: “What- why?”
Me: “Bad knees.”
Not Me: “Why?”
Me: “I have lupus.”
Not me: “What’s that?”
Me: “You know how your antibodies are supposed to be assigned to different things to fight- chicken pox, malaria, whatever? Well, a lot of mine are unassigned, so when anything goes wrong like stress or overexertion, these guys freak out and go attack a thing… Usually me, usually my connective tissue like in my joints. It hurts and makes me tired, makes it hard to think. Sucks.”
Not me: “Oh… Bummer. Can you fix it?”
Me: “No. Too much research going into cancer and AIDS, not enough into lupus. But, I can take the elevator.”
tah-dah. I suggest you get a spiel down.