Do I recall you take an SSRI drug and for a long time too?

This is what happens then:
The cells in the brain reduce serotonin manufacture (because the serotonin is being kept in the synapse all the time), and serotonin is the precursor to melatonin the sleep hormone. It's cofactor is methylcobalamin (methylB12 --which is the active form) to make it.

One side effect of chronic SSRI (like prozac) use is low melatonin. If you get up and expose yourself to light in any form during the night, you will stop making it also. There are melatonin receptors in the retina of the eye that sense light, and shut off melatonin manufacture.

What this means is that:
1) if you are low in B12 you cannot make melatonin

2) if you take an SSRI drug every day, you will make less melatonin anyway

3) if you expose yourself to any light during the night, the melatonin synthesis will stop.

4) melatonin is your sleep hormone. If it is broken, you don't sleep normally.

The final result is erratic and poor sleep.