I use to worry about this pretty often. I can go months and be doing fine and then one day I can wake up and my world is a mess mentally, I can still clean daily, make dinner etc , but if I had a job to be at I know I would not be able to manage. I am not on SSDI just due to Bipolar and all the fun stuff that it includes but also serious health issues..
My T has told me just because I can function well sometimes doesnt mean I no longer qualify, I havent been IP in 3 years and I got a review last year and I got a letter back in 3 -4 weeks later saying that no further info was needed and I would continue as is, If you come up for review keep in mind your pdoc and T or social worker/ case worker has to fill out there portion on how your doing.
Yes I worry about it I wont lie but I try not to think so hard about it..