The most intense and near death came from inserting a small rock of cocaine directly into the anus.
Beyond the feeling that my heart was about to explode, the medicine warned me not to "ingest" in this manner again. But she also taught me how to survive the overdose.
She told me to place and hold my mind in a state of truth. I was taught that Truth occurs when both hemispheres of the brain are firing in synchronicity and can be felt through observing stillness in the body and mind. Subtle, symmetrical motions in the frontal plane (yes motions) indicate that both halves of the brain are in simultaneous agreement (as mediated through through the corpus collosum). Asymmetrical motions, anything but "yes" occur when the motor fibers are not firing simultaneously. Interestingly, these motions can be felt in any position, sitting, standing, lying down, etc.
It took a few hours to recover and to my knowledge, have no lasting damage to my heart or body. But the best part is that my truth detector remains intact. In recent rears, I have taught a few dozen people (mostly meditators and yoga practitioners) to sit quietly and observe their mind and their subtle internal motions, so they can see themselves and evaluate the quality and truthfulness of their own thoughts.