It is not a medical, it is an assessment of functionality gauged against the PIP descriptors.
You will not be granted a PIP award just for having a medical condition, diagnosis or illness.
To receive an award you need to show that your condition or illness impacts on your daily activities and or mobility and to what degree when measured against the descriptors
Sometimes it is hard to think about our limitations and even harder to write them down or explain to a stranger how our funtionality is affected. The better you can do this gives you the best chance of receiving the correct award.