What kind of pain? Where exactly is the pain located at? What is your general posture like (full body pics from side & front could help)? At first glance it sounds like your attempt at tongue posture is encouraging your body to misalign in a way that pinches a cranial nerve, which is then alleviated by allowing the body to revert back to the former unoffending posture. If mewing makes you unbearably uncomfortable, it could be helpful to start fixing your posture from somewhere else. Hips, shoulders, feet, torso are all have equally crucial anatomical purpose. If one doesn't move well, nothing else will either. 

Hi, thanks for the response. The pain is a throbbing, sharp pain that feels like it emanates from the back teeth on either side, that shoot up to my head and sometimes down, giving me a neck ache. Initially I believed it was due to one of my teeth having a crown on it, but I started getting it on the other side too so it couldn't have been that.

I've been told my posture is great, no issues. I've been for AltasPROfilax before and there were barely any issues, just a slight offset between left and right, I've been for NCR and been told if anything I stand up too straight, he called it a military spine, but other than that I'm apparently very good, body posture wise. When I'm at my computer, I sit with a pillow at my back to encourage a straight spine rather than lounging back.

I do a lot of exercise, yoga too and am very mindful of my posture when doing my sets and poses.

Well that definitely sounds like it could be nerve pain. Do you have unerupted wisdom teeth left? The pressure from mewing could be pushing an inconveniently positioned tooth against a nerve. 

I never had any wisdom teeth grow, I only have 28. Infact a lot of my teeth are still the smaller baby teeth. Those particular teeth where the pain emanates from are adult ones though and my dentists have never made any mention of any unerupted wisdom teeth.

What nerves are in that area that would be getting trapped and what sort of things do you think I could do to alleviate any pain I feel?

Posted by: @Savage

Pretty much every time I try to adopt proper tongue posture, a few hours later, or a day or two, I'll get some seriously intense tooth and headaches that don't go away unless I adopt a bad tongue posture for a few hours, by that I mean dropping my tongue from the roof of my mouth to just floating about in the middle, with none of my teeth touching. No pain killers relieve the pain, nothing stops it unless I drop my tongue from the roof of my mouth.

I really want to do this, I want this to work so much but it seems like my body doesn't want to change. I don't even press hard, I just place my tongue there gently and it fucks me up for ages afterwards.

Does anyone have any advice? Has anyone been through anything similar to this?

I had a similar experience when I started to (hard)mew three months ago. Apparently it was because of mewing, in my case. 10 days later, my last wisdom tooth erupted fully and the pain stopped.

I think you dropping the tongue and adopting bad tongue posture stopping the pain is just further proof mewing is causing some drastic changes (good or bad). Have your wisdom teeth erupted fully?