the one thing a person should NEVER ever actually do to themselves is crack their own c spine area. this can in some cases cause some pretty major consequences, even when chiros do this too there is always that inherent risk of possibly creating a huge problem where there really was none to even begin with? i really do think at the very least you just DO need an MRI or CT here just to get a better look at the vertebrae and down to the spinal areas to see if anything is not as it should be there? also getting a good solid look into that brain with a contrasted MRI really would be the best way here to see if anything you did or could have already been there is an issue in the brain, espescially with blood flow/vascular issues.
honestly, no one really knows just what is actually there or going on inside their own bodies until they get a much better "look' into a specific area with at least some form of good scan. and in your case here, a contrasted MRI done on both that c spine and brain(they can do this all at one MRI visit) really would be able to at least give that deeper look into the most likely areas for your headpain. you just really DO need that look in there to really 'know' anything for certain at this point. hopefully there is nothing major going on, but in light of the headpain and the neck cracking here too, well, you just need to make certain ya know? i myself would most definitely be doing this if i were in your sitruation right now. please let us know what you find out. FB