Anxiety About Sleep

I always feel anxious when going to work after a day off. I work at night from 4pm-11pm so I have no clue why falling asleep the night before makes me so anxious. I've taken double my melatonin supplements and I've had a pretty busy day today and I woke up around 8am and it's about midnight where I live. This always happens and I hate it. What can I do?! I have a sleep disorder and I just now got my sleep pattern back to normal after literally being nocturnal for the past month and I don't want to screw it up again by not sleeping.