Pulsing in neck while using pillow.

I usually sleep on my back.  I get a strange pulsing sensation in back of the neck while using pillow. Pulses are infrequent and always disturb my sleep. When the pulse occurs I feel like I'm falling down even though I am lying still on bed. Due to this, I now sleep using a flat pillow and cover only half of my back side of head on pillow leaving the neck space free and away from pillow contact. I do have some stiffness in neck and I need to keep stretching and lifting my head, shoulders and arms to relieve the tension. I hear a pop sound when I do that. My work requires me to sit in front of computer for 8-9hrs, I also use my smartphone a lot. Need help to understand what is causing this and what should I do next.