The potential for risks or adverse effects of intensive meditation is a topic that is not discussed as much as it should be.
Every person is different and each person’s physical and psychological tolerance for deep meditation and the shifting physical and mental states that it may provoke need to be considered carefully. If you have any acute or chronic medical concern, especially of a cardiovascular or neurological variety, please speak with your primary care provider and/or specialist to determine if intensive meditation is safe for you.
If you have any acute or chronic psychological or psychiatric difficulty, please discuss with your mental health provider whether or not intensive meditation is appropriate and safe for you. You may not want to begin any meditative practice, Zen or otherwise, without having these conversations.