Rembrant
I don't think you are way off track re the tension in your neck being caused by the way you sleep. I have woke up in the middle of the night with a feeling of my neck being stiff and unable to change position but I realize it is most likely caused from lying in one spot for a long time. Not overthinking the feeling and just allowing yourself to fall back to sleep is one way to avoid getting caught up in "what if?" thinking in the middle of the night.
Try to keep your thoughts from circling back on you and just believe that you are OK. This takes work to learn how to do this but with practice it will help you to stay off the merry-go-round of anxiety.
Be well,
Kitt