The last time I was headed for trouble (not sleeping, which is a very bad sign for me), I took Zzyquil along with my 1mg of klonopin and had no ill effects.

I had no prn at the time, however if I had had one, I would have taken that (assuming it was a prn that was sedating) instead of the Zzyquil.

So my experience has been good, but I would be very careful with how much you take.