In the matter of a few short weeks, we have cut usage by 38%?
Demand does not have to fall so much for prices to begin plummetting on a commodity. It is all about excess capacity. Even a small drop in demand (due to recession or whatever) means there is now a small excess of capacity.
When there is no excess capacity, the sellers can set their own price, and that price will climb until people think they can do without, at which point it will stabilize. This is what had been happening, more or less.
Now that demand has dropped a smidge, there is excess capacity. This means that the buyers, not the sellers, have the advantage. Supplier X won't sell it to me for my asking price, so I will go to supplier Y, who now has extra to sell, and is willing to give me a price break to "fill his plant." Supplier X then loses that customer, and has excess capacity, and wants to fill it -- and coaxes a different customer to take that capacity using a price break. And so on.
So, you get falling prices. Again, the excess does not have to be a lot to get the ball rolling, it just needs to be there.
So, yes, it is all supply and demand.