Applying for PIP is extremely stressful. If you apply for PIP it is much better to do it though an advisor. Someone who knows HOOW to fill in a form, you should use Citizens Advice is possible.
I was lucky, and used there is an excellent Benefits Advisor in my local Maggies centre, and since she started the job 2 years ago, she has obtained over 2 million in benefits for the customers. Just by filling out the forms correctly.