Sometimes for reasons I don’t know I start making a model and as i rotate it I notice it is inside out. Example, I was making a nose and as i rotate the nose I am looking from the inside. Hope I explained it well. Why does this happen? how can I fix it? The normals are okay.
digiman 
could be an Optical illusion, your brain struggles to know if its point towards or away from you, until you rotate it further around.
Are you working from reference pictures? If your side view is facing the wrong way this can happen.
make sure you’re also in orthographic view, not perspective. I know with subsurf and edges, the illusion Hazza mentioned happens alot for me.
Thanks for you replies. It is not an illusion though I know how you can get that impression Turns out CD38’s suggestion is correct. I have made several head models and It happens sometime. I ignored it and worked form the insdeout but the solution is easy bow that i know how to fix it. Thanks CD38
digiman