It depends what's behind your sleeping problem.
Mood stabilizers aren't meant to serve as a sleeping aid, but if you are Bipolar, and not being treated for it with mood stabilizers, racing thoughts, the brain in overdrive can prevent sleep or keep it minimal, I went with only 2 hours sleep per day for 8 months, but my mind was speeding, thought from thought,etc.
In the begining I thought it was insomnia, and would go away, but it worsened, the rest is a long story, but when I was DXed with Bipolar,given the mood stabilizer, the racing thoughts stopped, in the begining the pdoc would prescribe anti anxiety meds and sleeping pill if needed.
Over time, there are occasions where a person may need to use them too, but on an average, just being stabilized helps the brain settle, which allows you to sleep.
Maybe that's what he is referring to.
Mood stabilizers are not in the class of sleeping pills.
Some may have a side effect of making one drowsy, but would not be used as a sleeping pill.
Lots of luck, hope you get a good nite's sleep soon.