It looks like you have been using the inflate brush set to "deflate" .  This brush has a bad habit of deflating the brush in on itself so effectively you begin to turn the mesh inside out, this is why the weird blobs have the normals inverted as you can see in your picture.  Use it with caution and generally only use it for small deflations. Removing larger amounts of the mesh is better done with other brushes such as the clay strips brush set to "remove"