Sometimes when i turn my head quickly i get this immense pain in the base of my skull the pain only lasts for about 5 seconds. what does that mean?

A pinched nerve or: It it is possible that you have a higher-up cervical nerve (occipital nerve) that is being pinched with rapid/forceful head turning, but being 18, more likely it is a cervical muscle spasm. I suggest some warm compresses along with gentle range of motion/stretching to the affected side, and use of aleve/motrin for a wk or so. If not better, consult your doc. Good luck.

Muscle strain: It's probably a muscle strain. An easy way to alleviate it is warm compresses for about 10-12 mins.