Is it hard?
Most appeals are not going to be easy!
Do you have to prove extenuating circumstances?
Do you have to present evidence personally to a panel (I suffer panic disorder).
See instantsunshine's response above.
You don't have to present the evidence as such - you could just say that you hope it will speak for itself. (Panel members will probably breathe a sigh of relief at being spared a presentation!)
I think it would be advisable to tell the panel that you suffer from panic attacks.
Do you have a good friend or relative - or someone from the primary school - who could come with you, and help with answering any questions?
The Q&As can be found here:http://www.elevenplusexams.co.uk/appeals/