If your failure is judged to be solely to have been caused by your health issues, and you applied in advance for your uni's Extenuating Circumstances where you fully disclosed all of your health problems and how they affected your ability to produce coursework and/or exams, then the uni should already have adjusted your marks. These might include things like extensions for coursework and adjustments during exams (things like extra time, breaks, using word processing rather than handwriting etc). If this has been done, then your final marks should reflect what your marks are thought to have been if you had not had your health disadvantages.
If you applied for ECs and they were accepted but adjustments weren't adequate, then this may be grounds for an appeal. If they were accepted but no adjustments were made, this would also be grounds for an appeal.
Presumably you have been getting low-ish marks all year to have failed it. If you do appeal your final year grade, you will need to account for the reason why you haven't appealed individual pieces of work.*
You do need to speak to your Student Union urgently. As has been said above, every uni can set its own rules and the SU will have people who know their way round your uni's regs and their appeals process.
There absolutely is humanity in the system, but you need to ensure that you have fully understood and engaged with it, in the ways required.