Where do widgets go?

I have the classified theme. After removing a widget from the left column, -Listing widget, and it disappeared. Not in the list anymore. There was another widget did the same thing, but don’t remember the name anymore. Where do they go?? Not in the available widget list, not anywhere. Would anyone please let me know.
What I did I just dragged it out of the left column to the right where usually the widgets are kept and that was the last time I saw it.
Thanx for the input if anyone have any idea of these widgets vanishing. John