It can be really hard somedays. I have worked full and part time jobs. I can't claim perfect attendance. But I have never been fired for missing too much. However sometimes I find just taking it mentally moment by moment helps.
I also try to maintain a pretty strict schedule and daily routine. It helps me sleep, and once in the groove, I can get through bad days on autopilot if need be. I set alarms on my phone to ding for pills, going to bed, etc. it helps keep me on track and on time. I allow myself to modify if needed but I like to stick to it. I find myself feeling more comfortable and stable in a life schedule.