Many of our members have lost the natural lordotic curve in their cervical spines which causes straightening of the cervical spine (military neck or forward head posture). That in turn can bring the styloids into closer contact with nerves & vascular tissues in the neck when a person is upright.
Your symptoms worsening when you’re upright suggests to me that you may have a straight or even reverse lordotic curve which exacerbates your symptoms when upright. If you have 3D images of your CT scan & are willing to post a few that show your styloids, IJV & cervical spine, we can let you know if we see that problem or you can look for it yourself. The good news is the neck curve can be restored by doing simple, gentle exercises.
This discussion thread has good info about the cervical spine: List of my favourite resources on YouTube to learn anatomy
