Sorry this issue is a day late - for those of you not in the U.S., Monday was Labor Day, a national holiday celebrated in true oxymoronic style by not working. I wonder if there are any holidays that people celebrate by working especially hard? Probably not.
Go Back and Forth Fast in Preview
If you're reading a PDF in Apple's Preview software, and you follow a bookmark or an internal link to move around within the PDF, you can quickly return to where you were by pressing the keyboard shortcut Command-[ (that's Command-Left Bracket). Or, you can choose Go > Back.
The command works iteratively, so you can go back to just the previously viewed page or if you issue the command again, to the page before that, and so on. There's also an equivalent Go > Forward (Command-]).