I don't think there is an answer to your question. Side to side, front to back, up and down, they all have movements but unless you did them continuously for many many repetitions, I doubt they would make any difference. I have told you this previously. Sub-concussive impacts cause damage when there are hundreds of them over a relatively short period of time

You are asking hypothetical questions that do not seem to have a legitimate purpose. Are you planning on an activity where you would need to repetitively move your head back and forth in any of these directions ?

Tearing axons is not the only way a concussion manifests. Plus, axon shearing is not necessarily an immediate event. The axons can be strained resulting in slow deterioration. You said "Or is the odds of tearing axons greater with up/down movement? I recall that's been said." I don't recall anything like that.

Nobody is going to test somebody by having them move their head repeatedly to see if it causes any damage. The only live concussion testing done is done on rats. The research done with football players is not accurate enough to pinpoint the difference between concussions caused by different directions of force.

Are you getting any serious counseling for your OCD ? You really need somebody to help you let go of these concerns. I don't think any amount of factual information is going to change your OCD regarding this. Your mind will continue to find a new way to obsess about these issues.