Have you ever been using Lightroom, editing your way through a collection of images, only to suddenly realize your "Detail" panel is gone, or your "Presets" panel has disappeared? If it hasn't happened to you, it may happen to you eventually, so I want to share this simple fix to prevent you from having a similar freak-out like I had. ;-)
How They Disappear
Lightroom side panels are hidden when you right-click over the panels and click on one of the panel names (that have a check mark next to them). Usually this is done by accident. You don't mean to make a panel hide, it just seems to accidentally happen. Mostly likely when you have gotten a bit ahead of your computer, but you don't know it yet. I don't know. But don't feel bad, and know you are not alone.
Also, this phenomenon can happen in both the Library and the Develop modules, but for me it's happened more in the Develop module.
Bringing the Panels Back
The good news is that the panels aren't gone forever, they are merely hidden from view. There are two ways to get them to show again, one which is quicker than the other.
The first method is to right-click over one of the panels that are showing, which will make a small drop-down menu appear. Simply click on the one that is missing; it will NOT have a check mark next to it.
The second way to bring the panel back is via the main menu at the top of Lightroom. Click on Window (shown below), then Panels, and lastly on the panel you are wanting to see. The missing panel will instantly appear.