I think your idea about neck position is valid. If you could lie down without a pillow to lift your head but just enough to support your head on each side, you may find an improvement. Neck/cervical inflammation can reduce blood flow. It can also cause muscle spasms that increase head aches.

Work on the neck posture idea and I bet you will see an improvement. Your anxiety is also something you need to find a solution to. When I need to rest, I need something low stress to occupy my visual and auditory processing. I watch good music videos like Celtic Woman. I have a small selection of music and videos that allow my mind to pay attention but also relax.

These stimuli take the place of stressful thoughts. It would be worth a try. I even watch reruns of movies. Enough to occupy my mind but not stimulate me.

You will need to experiment to find what works for you. The effort will be well worth it.

Are you following a vitamin and supplement regimen ? It can help you brain relax.

My best to you.