I have fibro and get Pip. Told them about difficulties in my mobility and daily living, I got it uncontested. It's just a shame we get good days and bad days because they don't see it as continual illness.
I did an appeal for a neighbour (cancer) and I went into more detail and what he felt was wrong on their report, I contested and gave an example of why their opinion was wrong and how it actually affected him in daily life. Example he has mobility and can get around- so I told them about the affects the radiotherapy has on him which can sometimes leave him in bed etc
I have always been advised that you should always fill in the forms as though it's your worst day. With regard to the PIP form, it's useful to look up a guide online and then you can make sure the info you are giving actually answers the questions. I believe that you are unlikely to get the mobility component if you can walk 50yards or more, but you should get the daily living component if you struggle with washing and dressing etc. Hope that's helpful, good luck with it.