How to apply the multiresolution modifier from sculpt mode? I'm kind of new to blender, I've been using it for about two weeks but haven't used sculpt mode much. 

Today I decided to sculpt the head of a character, using a multiresolution modifier to help get the geometry I wanted, but I can't apply the multiresolution while in sculpt mode and if I leave sculpt mode my object turns back into a low-poly model. 

If I apply the multiresolution in object mode then all of my sculpting is gone for good. How in the world do I keep my sculpting work while in something like edit or object mode?
You need to raise the Preview value to match the Sculpt, and apply the modifier in object mode.