I Am A Female, 68. Since November, I Wake Up

I am a female, 68. Since November, I wake up during the night with the feeling that I'm hanging upside down. The moment I stand up, I feel the sensation gradually disappear. I have had Head Scan and MRI and there is nothing abnormal. I also had a spinal tap which revealed everything normal. I do have pain in my neck and upper spine when I lie down on my back. What could be the cause?