I am so sorry that you are experiencing this. I don't know that I have experienced the same thing at least not for such a lengthy and consistent way but I have often experienced periods of time which as you describe is like a 'mental veil' and these episodes have varied from days as at time to parts of days. There are days when I am at work that I have felt this and somehow just float throughout the day without achieving anything. Somehow no one has ever noticed as I seem to be able to make up the workload on the days when I am good.

I don't have any answers but I thank you for your post as it has clarified for me that this is a distinct experience/symptom and not just my imagination.