Your joints are releasing the synovial fluid and makes a cracking noise.
Why does your neck crack?
I only know of a few you can pop the neck by having the person lie flat on the floor with you sitting behind them. You place one hand under the head and the opposite hand thum along the jaw line...
It can cause a whole lot more than just biploar disorder. That stuff will mess you up for life.
Paralysis from the neck down is usually cased by a broken spinal cord.