I'll give a quick explanation of what seems to be happening. The ligaments in the next are what provide support to the neck. When you "pop" or "crack" your neck, you are stretching out those ligaments. Over time, the ligaments lose their spring like tendencies and become "weak". To provide the need support, the muscles of the neck have to step up and assume the role. This puts extra strain on the neck muscles and they become tense and tight and stiff. This leads to a detrimental cycle: To relieve the pain and stiffness in the muscles, you "crack" your neck thus stretching the muscles but it also stretches your ligaments as well further weakening them. The condition in which your ligaments become weak is called hypermobility. This is because weak ligaments are no longer supporting your neck as they should.
This shouldn't scare you because there is treatment. What most doctors will do at first is have you perform strengthening exercises for your neck muscles. The stronger the muscles, the easier it is for them to support the neck. The easier it is for the muscles to support the neck, the less pain (or no pain) you will experience. This will do away with the stiffness and tightness you feel. It seems that your shooting pain and spams are due to the fact that your muscles are weak and you have a limited range of motion. Exceeding that range of motion, causes extra strain on the muscles. With exercise this can be corrected. I strongly suggest that you stop cracking your neck and see a medical professional for treatment.
I hope this was helpful.