I took Seroquel PRN for sleep but I was told if my mood seemed especially down, I could take an extra dose for a few days on top of my regular AP. I've heard of doctors prescribing it that way. The concept of an "emergency medicine" is a good way to kind of think of it used for those situations I think. Seroquel is rather sedating in my opinion but can seem to have a good effect on mood stabilization even at lower doses.