This indicates a likely unconscious anxiety / fear towards plane traveling. If so your body would spend the duration of the trip in high stress mode (over engaging the sympathetic nervous system, which can be measured by lower than usual HRV) as it’s expecting danger. Relaxation techniques before & during travel (like meditation or repeating a mantra often) or hypnotherapy session to have new associations with plane travel are likely to significantly reduce the excessive impact of plane travel. Some find that taking prescription anxiety medication before getting on the plane help as well.