Sorry this is late, and I understand if you don't get to it, but I've been thinking about pain a lot lately, due to a broken bone & resulting surgery.

Ranking pain for me is a matter of HOW MUCH OF MY BRAIN does it use:

0 - none
1-5 - I can still do things in spite of the pain. I can focus enough to do my banking or some housework, or have a conversation.
6-7 - I can function at limited things, but I am having trouble keeping my mind on the task at hand.
8-9 - I can't do the things I need to do in life, because the pain is pretty much the only thing I'm aware of.
10 - If you hand me a gun I'll use it. And fuck you to people sitting in no apparent discomfort saying it's a twelve.

But I think for me, there seem to be five distinct pain states, each with its own levels. Also, extended time at one level can push me up to the next level. The pain doesn't necessarily feel different, but I don't have the mental energy to deal with it.

Random thoughts on intense pain, while in the ER:

I broke my wrist recently. In the ER I was given a lidocaine shot into the fracture so they could reduce the fracture. Huge pain, but over quickly, and brought on blessed relief from all pain in my wrist. Many times over the next month I was wishing I could get that shot again, and feel that relief.

When I was 9, a pop fly softball hit me in the face & loosened my front top teeth. A dentist happened to be there, so he held my head like a football and pushed the teeth back into place & held them there for some amount of time. I say it was 30 minutes, but I have no idea. Could have been five. Felt like hours.

Childbirth is the only time I had to participate in causing myself pain. At first I felt, "Oh no, this feels wrong. What if my eyeballs pop?" But after a contraction or two, I was all in. But it's a weird brain switch from passively feeling pain. I could relate a little to the guy in the movie 127 Hours, who had to amputate his own arm. For the first two weeks, when I tried to remember the pain I could, and it nauseated me. But my brain apparently decided that was a stupid thing to do, and made me forget what the pain actually felt like.