I was doing a solo nav when whilst looking inside the cockpit briefly at my chart and then looking outside again, I got disorientated.
Do you suffer from any form of Vertigo? Its quite common amongst pilots but is not usually an issue in an aeroplane. Suddenly moving your view from inside to outside could trigger a reaction. A low flight over the edge of a cliff can have a similar effect, like someone with Vertigo standing on the edge of a Cliff, the brain tries to rotate the picture. Keep your eyes outside, and only glance in for a few seconds, something that should be taught in navigation anyway.
With more experience in the air you brain will adjust so don't give up, its something most people can overcome. Maybe a little basic instrument flying training would help, as its purpose is to teach you to ignore your sensors and believe the instruments.