What Is The Popping Sound When I Bow My Head?

Good Evening, I have a question. I am a 21 yr female weiging at 190lbs. Not everytime but more-so then others, when i bow my head or hold it down, it has a poping sound and a feeling to it like a knuckle pop. One time I was driving and i let my head down at a stop light and it popped and I promise I felt it shimmer in my fingertips. Is something back there not aligned right?