I don't have it, but I thought I'd pipe up as a friend does.
She describes it as having 8 (I don't know why '8') different types of pain, firing at high intensity all the time. She says it's like being burned, frozen, stomach ache, headache, cramps, stabbed all over, etc, constantly. When she takes a painkiller, it might take away one, but all the rest stick around.
For those saying it's fake, or a made up illness, you'd only have to look at her to know it's real. Imagine how someone would look if they had just been beaten up again and again, and due to that pain, literally slept an hour a night because they physically couldn't manage to stay awake any longer, waking up again because of the pain.
Don't get me wrong, many people DO fake it, because it can't be proven and it's easy to say you're in pain, but the real illness, whatever it is, I wouldn't wish on anyone.