mcquade
Even though you are only receiving NI Credits, this only happens because you have previously shown that you meet the criteria for an ESA award, the re-assessment is to see whether you still do,
I can't explain why you are being re-assessed after only a year, although it is likely that the timescale is related to an expectation (realistic or not) that your health may improve.
If you want to continue to receive the NI Credits then you need to complete the form in detail and supply evidence as you can, even if they have previously been supplied to the DWP.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems