It happens because of a hypersensitivity of the nervous system which becomes hyperconscious and responds this way, especially when it engages in internalising activities.
You may try the following.
1. Nadi shuddhi pranayam or simple deep breathing a few minutes before you begin your meditation.
2. Ensure you have enough fluids and salt.
3. Call Peace before you begin the meditation.
4. Try sitting in a comfortable chair for meditating.
Affectionately,
Alok Da


