Hi Jason,
This is kind of non-obvious, isn't it? What you inadvertently did was activate Local Tab Order, which isn't quite the same as reversing the tab direction. With CTRL-SHIFT-O, you set the field your cursor was in at the time on that screen as the tab exit point. To undo it, while in that same screen and with the cursor in one of the fields, hit CTRL and right-click. You'll get this menu:
Select Configure Local Tab Order (or hit SHIFT-CTRL-L), and in the next screen you'll see the field technical name listed as Exit Point. Hit the Delete button to the right of it to clear the tab order back to default.
That should fix it.
Cheers,
Matt