Hi Kellie, I am very sorry to hear you're suffering such anxiety. From what they said to me and information on the internet it seems if you were out of the country and/or unwell they cannot penalise you for returning the form late. You just need to explain why on the back of the form, where it asks. Just try to get in completed within the next week if possible. The guide on here I'm finding most relevant for completing the form is the guide for mental or physical conditions: whatever applies to you. Also try somewhere like a law centre, the CAB or MIND if you need help with filling in the form-there is a list of organisations that can assist in one of the member's documents on this site. Good luck with it.
I've found the document for places that can help you fill out the form, it's called Getting Help with your benefits and it's under General benefits info in the members section.