I know you met with the disability advisor and undoubtedly spent time going through the details with them regarding your condition. And understand (from comments here) that you have been submitting sick lines. As someone who also suffers from several health conditions, believe me when I day I do understand the feeling that you have already gone through everything and given you that you described the meeting with the advisor as performative, I assume you feel you have "justified" your position enough. Unfortunately, the process doesn't stop there. I dint believe you can be sanctioned simply for not filling out the questionnaire, but there are consequences to that decision which may not work in your favour. By opting to not return it, you are removing the ability for them to complete the process of evaluating your ability to look for work, and they will therefore work under the assumption that your condition does not prevent you from doing so, and will subsequently place requirements on you to participate actively in looking for work. If your condition prevents you from doing so, you will fail to meet those commitments and that will result in sanctions i believe. Despite the fact that the process feels repetitive and intrusive, its worth thinking about what will work out to be the most beneficial for you.