I don't know much about Pip assessment but think it can be a mine field. Maybe contact PD UK admin or post a direct question on here.
I've managed to do the PD exercises a couple of times but it's not the same as a class.
Finding a good PD nurse can be crucial as if they can't answer your questions they will find out. Also they can be a middle man between you and your consultant.
Can you speak to your human resources department to discuss reducing hours? It takes a while to get your work /life balance to where you are stress free.
Sorry I'm not much help with PIP.