I doubt you ever suffered a concussion. Your kevlar would have spread the impact to your neck. Your symptoms sound more like a upper cervical injury which you acknowledge. A vertical compression to C-1 and C-2 can manifest with almost every standard concussion symptom.

Lifting weights and impact exercises can be hard on upper cervical injuries. Weight lifting causes muscle tension in the shoulders and neck.

You are correct about not getting good blood circulation. The vertebral arteries can be compressed by inflammation in the C-1 and C-2 area.

Unfortunately, C-1 and C-2 are not faceted vertebra, meaning the condyles do not snap or center back into the facets very well. Condyles are the convex portion of the bone. Facets are the smooth slightly convex depressions that the condyles slip into allowing movement.

The ligaments that hold these joints together can get stretched and leave the joint unstable and subject to strain and inflammation.

Some have used prolotherapy or PRP or stem cell therapy to encourage strengthening of these ligaments.

The most important part is to limit straining them when they are not properly supported. Sleeping with a crooked neck is a big problem.

Inflammation in this area can impact quality of sleep than can cause many of the symptoms you mention.