As soon as I sit down to meditate I produce continuously gas and experience heartburn and burping. It does not stop even when I enter a deep state of stillness. What can I do about it?
There are various ways to address your question. First, it would be important for you to have a check-up from a physician.
Digestive problems like this, no matter when they are occurring, may be something you need to take care of medically.
Many things happen when we begin to meditate deeply, which have to do with a purification process that is happening — things like excessive saliva and the need to swallow, eyes watering, sensations of heat or cold, and so on.
Purification is a good thing! And these things generally will pass away with time. Plus, they are often a sign of tension in the body. Trying to relax more deeply, expecially in the body part(s) most affected, should help.
The Energization Exercises before meditation will also be a great aid.
Of course, praying for help from your Guru is very effective. The best prayer is not: "Please make this go away!"
A better prayer would be: "Please show me what to do to alleviate this physical challenge, or if that is not possible, how to get beyond it."
It is wonderful that you are able to "enter a deep state of stillness" even with all this going on. Amazing really, and for that you should be grateful. Grace is happening!
Finally, you might want to consult Swami Kriyananda’s book The Art and Science of Raja Yoga. In the "Health and Healing" sections of each of the 14 Steps in this book, there are truly wonderful suggestions about yoga postures and various other techniques which are great aids for the digestive system.