That chart pretty much sums it up for you lazies, so that you don't have to read multiple paragraphs trying to figure out what I'm saying. Basically, any skin type can become dehydrated, including oily skin. It's caused by external factors, where dry skin IS your skin type, and that's just the way it is.
Before I got this facial, I noticed that my skin gets somewhat oily throughout the day, like normal, but random dry patches were showing up on my face. I would get dry around my nose, mouth, eyebrows, and hair line. I think the cause of my dehydration was the cleanser I was using (Yes to Cucumbers Calming Facial Cleansing Gel), because I switched over from the Yes to Carrots Daily Cream Facial Cleanser and did not have a problem with dryness at all.
Exfoliating is essential. You can moisturize all you want, but if you don't get rid of the dead skin cells, your moisturizing will only help the dryness on the surface.
If your skin gets dehydrated often, it might be good to invest in a good facial hydrator, which is something you either mix in or put on before your apply your moisturizer. The hydrator will help replenish nutrients in the skin and pull your moisturizer deeper into your skin so you get maximum moisture. The only one I've tried is the SkinCeuticals Hydrating B5 Gel, and it worked amazingly for me but I'm sure there are cheaper alternatives.
Drink a lot of water. Probably didn't need to be said.
Stop using any facial products that may be harsh on your skin. Look especially for products with hyaluronic acid in them, which will help the water bind with your skin. I started using CeraVe's Hydrating Cleanser with hyaluronic acid and it's definitely helped to keep my skin hydrated throughout the day. Look for other products such a moisturizers or skin boosters that contain hyaluronic acid.
I hope this helped clear up some confusion! Has your skin ever been dehydrated? What products do you use to keep you flake-free?