What Causes Stiff Neck After Stretching?

Hi, this morning I woke up and did a quick stretch and as my head went back a little, I heard this internal crunching noise in the back right side of my neck. It hurts very badly now, like I have a stiff neck that won't away. I am a 27 year old female in good health. Can you please tell me what possibly happened and how I should go about taking care of it. Thank you!