Pilots are taught to not rotate their head around during maneuvers, so the head should stay exactly as it is and not stabilize in Relation to the outside horizon. Of course people do this from time to time and especially when they are activly looking outside the aircraft but most of the time, at least during normal, non-intensive maneuvers, they will not stabilise their head in regards to the horizon.
Tilting the head during maneuvers in real can cause things that are not possible to experience in a simulator.
Overall you will find plenty of videos online where pilots will tilt and rotate their heads when they look outside, but will remain mostly straight when they do normal maneuvers. Both versions are around and there is no definitive answer to which behaviour is correct.