Appeal.
They do this all the time.
You need a huge amount of medical evidence and you also need to record the assessment.
You need to tell them in advance that you will be recording it.
I bought three digital voice recorders. Put two on the table and had a third nearby that I started recording just before she arrived (I had my assessment at home). At the end of the assessment I let her choose one of the ones on the table and I kept the other. And the third I hadn't told her about just in case something accidentally happened to hers. Paranoia or good planning? 😁
Anyway, I was awarded enhanced rate daily living and mobility for an ongoing period or words to that effect. That's where they check on you every ten years or so to make sure you're not dead yet.
Don't push yourself to do things. If they want to push you or you push them or you do something physical which you know will hurt - don't try to be a hero. Say no I can't do that, it is too painful.
Remember that they are not on your side. They'll act all pally pally but they're looking for anything to use against you.
If you are going to an assessment centre be aware that your assessment does not begin when you sit down in the interview room. It begins in the car park. In the waiting room. You can walk down the corridor to the interview room? Clearly you don't have trouble walking.
Be completely honest.
Record everything and give them a copy.
Supply enough medical evidence that you have Greenpeace holding a vigil outside for lost trees.
Don't push yourself to do physical tasks for them if those physical tasks will injure you.
Have someone with you.