Air carrier First Officer reported descent below glide slope on approach when the Captain experienced spatial disorientation.

Narrative

On Aircraft X operating from ZZZ1 to ZZZ; we were conducting the arrival and approach to RWY XX at ZZZ. During vectors for the final approach; the Captain called the runway in sight and began maneuvering toward a visual final.At that time; I did not have the runway in sight; so I continued to back up the approach using the ILS RWY XX for situational awareness and vertical guidance.As the aircraft was turning toward final; I observed that the turn was being initiated prior to the final approach course; and the aircraft also began to descend below the ILS glide path. I immediately made a verbal callout regarding the early turn and a separate callout that we were going below glide slope.The Captain acknowledged the callouts and stated that he was experiencing spatial disorientation. He then elected to discontinue the visual maneuver and return to flying the ILS RWY XX.Once re-established on the ILS; the approach was stabilized. The aircraft met stabilized approach criteria at both the 1;000 ft and 500 ft gates; and we continued the approach to a normal landing without further issues.CRM and communication were effective; and the deviation was promptly recognized and corrected with no loss of safety.