So what I understand correct mewing is obvious by muscles under your mandible rising up (sucking up). This happens when you contract muscles in correct way and tongue gets sucked to mandible.
Problem is - I cannot hold this position more than 1 second without gagging instantly.
It's like holding a swallow mid-point forever. How is it even possible?
30 yo, need to expand palate, move maxilla upward and forward, reduce gonial angle.
Try your best, your body will accommodate to this posture