A:    

  The first thing to do in this situation would be to cut back on the practices that you are doing. If you are using any mudras or bandhas, or advanced pranayamas, then these would be the first to cut back on. If you are still getting symptoms of discomfort, then reduce the timings of your practices until you find a comfortable level that works for you.

  Some people can be very sensitive to mantras. Or, that sensitivity can develop as they progress with their practice, to the point where the vibratory effect of the mantra is too stimulating for the subtle neurobiology. If cutting out the most stimulating practices and cutting back on the timings of the basic practices still does not help, then you can switch temporarily to using the breath as an object for meditation. 

  These are the instructions for practicing meditation with the breath: 

  Start by sitting down with your eyes closed in a comfortable position. You can let your hands rest gently on your knees or  place your hands on your lap, palms facing upwards, one hand on top of the other. Let your breath be natural, breathing gently in and out through your nose. There is no need to slow the breath down or speed it up, or to breathe deeper than you would normally. Bring your attention to the breath simply flowing into the body, and flowing out again.

  You can be aware of the breath either at the nostrils, or deeper down in the body as it fills the lungs, or you can simply be aware of the whole process of breathing. People tend to find their own natural preference. If your attention wanders away from the breath, when you notice that your attention has wandered, easily favour the breath with your attention over anything else that is going on. 

  Sometimes there will be a natural pause between the in breath and the out breath, or between the out breath and the in breath. When this happens, simply be aware that the breath is suspended either inside the body, or outside it. There is no need to make this happen, it will happen spontaneously when the time is right and the body and mind are calm. Sometimes these natural pauses of the breath will be short and sometimes quite long. Whatever is happening is fine. You may find that the breath will slow down naturally on its own, or that it becomes quite shallow. Again, whatever is happening is fine and there is no need to interfere with the natural process. Sometimes the breath can become very subtle, so that we can hardly feel it or hear it and it may even appear to suspend completely. This is a state called kevala kumbhaka. Again, if it is happening it is fine, and is a good indication that the mind is coming to rest (samadhi). 

  With repeated practice you will find that the mind wanders less, and the natural, spacious quality of the mind becomes more apparent. Over time you will find that you are able to simply rest, being continuously aware of each breath coming and going. It is a very beautiful and peaceful state and gradually leads to the cultivation of bliss. After each meditation session take a few minutes to rest. This helps to ground and stabilize the energy in the body.

  As the practice is more gentle than using a mantra, you may find that you can go back up to 20-minutes twice each day with this practice, without experiencing any head pressure.

  If you do switch to using the breath as a meditation object, then you should remain with this new meditation object for at least 6 months. After that time, you can decide if you want to remain with the breath, or return to using the mantra.