Hi Deirdre
The first thing you need to do, if you are unhappy with the decision is to get a copy of your assessment report, so you can understand what the assessor said when you were assessed. If you want to put in for a Mandatory Reconsideration you have one from the date of your decision letter. I have only ever known two people to have an award downgraded at an MR. The majority of people find their award stays the same and 17% win their MR. Only you can decide whether it is worth the stress. If you want to move forward you need to contact the DWP. You can find details of putting in an MR in the guide PIP Appeals.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
