That's the thing there is no error message, it has simply erased everything that was in the Scene View. Before that I had a model of a house with lots of furniture and such, and it's all gone from the Hierarchy Window, along with my empty gob's that had the mainCode for the game attached to them. The assets and everything are still there in the Project Window. All I did was imported a custom-package I'd made containing a humanoid model with a few code scripts attached to it. Once imported it obliterated everything that was on the stage and replaced it with scene from the other project. When I imported my custom package, I remember it asked if I wanted to update external files or something- wish I could remember exactly what the message was.

Also, I'm not sure if it was there before or if it's even relevant but I do have 'PREVIEW PACKAGES IN USE' on the top.

Thanks for your help.