Maybe it was something you said, maybe it was something you didn't say. But it has happened, your Browser Bar (the area of your model history) has run away. Before you start plastering milk cartons, check out the User Interface fly out. This is located on the View Tab --> Windows Panel.
The most common reason you lose your browser isn't neglect or verbal abuse to your computer, but perhaps a small little box that inadvertently gets picked if you have had too much coffee today and find yourself clicking on your screen a little too wildly.