To confirm svety's comments: questioning is designed to ensure you fail the test! For example during my PIP appointment I was asked to stand on one leg then the other - this I CAN do BUT, if I do I will be bedridden for several days (osteoarthritis). The design of the question converts it to an instruction which I was left feeling I had to comply with.
My daughter was a CAB benefits adviser and warned me about this ploy. The solution was to [politely] say "Sorry, I can't because ..." If you simply refuse then they view that as being obstructive - you have to give a reason.
I was asked once, "How far can you walk?" Well, in reality the answer is probably several miles BUT the choose not to include 'without extreme pain and in a reasonable time' - given that I take strong pain killers every few waking hours to dull the pain the answer was actually "No distance at all"
The numbers claiming benefits hasn't suddenly reduced because everyone got better but [mainly] because they redesigned the questions being asked - that is why you ABSOLUTELY NEED some help from benefits rights groups/CAB etc.
Think about what you used to do that you can't do now - work through a 24 hour period. Can you jump out of bed in the morning and throw the curtains open (or does the effort of moving your legs down leave you breathless), can you still skip to the toilet or is it an effort using walls for support? can you eat and drink without a problem, walk, talk, socialise etc, etc? Get the idea?
Whatever you claim they will most likely reject the claim [that's fairly normal] - read the appeals process and follow it - your advisor will guide you.
In the drive to stop the benefits cheats government has harmed an awful lot of genuinely sick and disabled people - your claim will be a major project filled with highs and lows but you have to remember, many people simply give up, then the government wins!
Having said all the above, in my case I was invited to assessment, assessed and a decision made in just over three weeks - and my claim was actually increased! Sometimes it does work - I hope it does for you.