@blistle Well, based on your symptoms and limited imaging you provided, I can safely assume, you are suffering from Internal Jugular Vein Stenosis (IJVS) symptoms. This, I think is due to compression of the Styloid fragment on your right IJV and since your left IJV is small and is also compressed by the C1, it can’t compensate it. I think your symptoms are so similar to mine (see here Visual snow and floaters - #4 by KoolDude), no surprises there because your IJVs are like mine, just the opposite. I have smaller right IJV and dominant left one which is compressed by the Styloid & C1.
We can tell the collateral dilation by looking at their sizes. In a normal Scenerio where Jugular vein is fully open, they will be just tiny vessels and will not be prominent. Also, there is a network of veins that attach to the Jugular vein (primarily condylar veins) at the base of the skull and it is called Sub-occipital Cavernous Sinus (SOCS or SCS) or Sub-occipital Venous Plexus as it is sometimes called. It serves as the bridge where the Condylar veins (from Jugular vein) connect to Vertebral Venous Plexus (VVP) which is an alternative path for draining the brain/spinal cord mainly when you are upright but usually do not drain when lying in supine position. Since you were lying down in supine position during the CT Scan, that is when your jugulars primarily should be draining your brain. But in your case, they are impaired so blood gets rerouted to collaterals (Condylar Veins) via SOCS which is swollen (see the blue circle - what appears to be a tumor at the base of the skull is the dilated SOCS) in your case due to over-drainage from impaired right IJV and finally to VVP (Cyan Arrows) which is also bit dilated visibly. You can read more on collaterals on this study (https://www.frontiersin.org/articles/10.3389/fneur.2020.00913/full) if you want to learn more
Here is the dilated SOCS (Blue circle with arrow) and dilated VVP/deep cervical vein (Cyan Arrows) indicative of impaired Jugular vein or as it is known Internal Jugular Vein Stenosis (IJVS).
Here is an internet image to show you how the jugular vein interconnects to SOCS or as they call it in this image Sub-Occipital Venous Plexus (SOVP) which is the same as SOCS.
Here is another image from a study that compares lying down (supine) versus upright jugular drainage. You can see where the SOCS is on this one. See how prominent the SOCS become when upright versus when supine. So you should not see dilated SOCS/Collaterals in supine position is the take away here, if you do, that means your Jugular vein is impaired.
One final note, the muscle tightness and weaknesses are thought to originate from the dilated collaterals/SOCS which can cause compression or venous hypertension on spinal cord which then can can cause muscle weaknesses/tightness…etc. You and I fit this. In extreme cases, it could potentially mimic myelitis cause paralysis on all four limbs.
Well, I think you need to do Dynamic Catheter Angiogram/venogram with manometry to quantify the degree of narrowing on your jugular vein. This is not necessary though if you have capable ENT Surgeon that is familiar with Vascular ES. I would recommend you to contact Dr. Hepworth who is by the far the best for Vascular ES involving Jugular Vein. He also does the Catheter Angiogram/venogram before operating on you. Do not waste your time with ENT folks who lack the knowledge of this rare disease. They will give you the run-around and dismiss you. You can save both time and money by contacting the right ENTs who operated multiple folks with the same IJVS. Dr. Hackman is another good ENT surgeon. You can also follow the advice of @Isaiah_40_31 regarding mitigating the symptoms of this while seeking intervention.
On finale note, I am pretty sure you have IIH signs but I would like both the CT and MRI (If you have one) to examine. There is a free anonymous site where you can upload the images. This site (https://www.dicomlibrary.com/) will strip all the identifiable fields before uploading the images and it is good way to share all types of imaging. The only downside to it, it takes long time to upload if you have slow upload connection. Also if the CT/MRI is way too big. But you can also share individual slices like Neck CT sequences only instead of the whole CT. There is also tutorial on the site on how to upload and share it. This is optional. Only if you want me to give you more raw CT slices pinpointing where the compressions are on the right IJV.
Wish you luck. I hope this was helpful.