People tend to slump over when they meditate. The head drops and shoulders slump. This posture closes the chest and throat in a moment where you want maximum airflow.
Here’s a quick tip:
Halfway through the session take a moment to check in with your posture and body position. After the check-in, if you are feeling constricted then imagine a soft claw coming down from the ceiling. It’s the same kind of claw that you see in the arcade machine that grabs toys, but the grip is so delicate that the toys end up falling.
Imagine the claw slowly grabs your head and starts lifting you up. Your neck extends, your chest opens up, and your spine straightens. Just like in the arcade the claw slips off your head and retracts away. Your posture is now open, upright and relaxed.