Please dont panik, they are sending everyone who is claiming income support, DLA, ESA or incapacity benefit for this assessment, it is the governments way of trying to de complicate the benefit system so everyone is on the same new benefit, only at different levels depending on your ability to work.
I have completed the form you are talking about, they do not take much notice of what you put on it, it is more a way of them assessing the easy targets(those who send it back quickly) and the evaders (those who do not reply then complain when their money is stopped)after stating on it that i am unable to mobilise my wheelchair outside at all, i have been called in for an assessment. they are considerate and send you details of the route to take to get to the assessment, even give you the timings for each bit of the journey, only problem i have had is the journey plan they sent me had me walk to a bus stop, get on a bus, walk to an underground station, get on an underground train .........7 changes in total taking over an hour! the letter also stated the assessment was on the 3rd floor, there is a lift, but it does not work in emergencies like a fire breaking out, so you can go but you are left to fry if the building goes up in flames!!!! (one way to cut the number of claiments!!)
After phoning them to say 11am with over an hours travelling before hand was impossible for me even if i had help i was told to go to my GP and get a letter stating i need a cab, after doing this and being told it would cost £35 for the letter and telling my GP where he could stick it I phoned them back and have been given a later date, later time and they are arranging a cab to take me to a different assessment centre!
so what i can say is persevere! going to an assessment will allow you to tell them more about how your difficulties affect you and how they effect your ability to concentrate, finish tasks etc.
I am hoping the assessors are savvy enough to realise those who are swinging the lead and those who are not, especially as my physical difficulties are caused by a mental health condition, yet i show no 'normal mental health signs' and do not have a physical diagnosis to explain why i am as i am.
My assessment is sometime at the begining of October, I will report on what it entails after i have been so you can be prepared.
I intend to take a copy of my care plan from my social worker and all the reports of the tests i have had and from the professionals who have been involved in my care, that should be enough to shut them up for quite a while I hope.
it is crazy the way this government are looking at what you can do rather than what you can't, there was talk of classing wheelchair users the same as walking people because they can mobilize around an office! no thought of how they get into the office though!!! if the government ran on brains we would be better off with a cage full of gerbils running the country!!!!
definitely talk to your care team about it, gather as much written evidence as possible to take with you, better to have too much than not enough. be/talk about you at your worst on the day of the assessment... exhaust yourself the day before, but be honest with them. I should think there is an appeals process you can go through if their decision is not what you feel is right. I know it is difficult just to function to do the basic living tasks at times, but you need to summon all your energy to tackle this.
Take care
good luck x