António R. Damásio said this quote

“ As a consequence of natural analgesic actions or as a result of the administration of drugs that interfere with body signaling (painkillers, anesthetics), the brain receives a distorted view of what the body state really is at the moment. We know that in situations of fear in which the brain chooses the running option rather than freezing, the brain stem disengages the part of the pain-transmission circuitry, a bit like pulling the plug. The periqueductal gray, which controls these responses, can also command the secretion of natural opioids and achieve precisely what taking an analgesic would achieve -- elimination of pain signals.In the strict sense, we are dealing here with a hallucination of the body because what the brain registers in its maps and the conscious mind feels do not correspond to the reality that might be perceived. Whenever we ingest molecules the have the power to modify the transmission or mapping of body signals, we play on this mechanism. Alcohol does it; so do analgesics and anesthetics, as well as countless drugs of abuse. It is patently clear that, other than out of curiousity, humans are drawn to such molecules because of their desire to generate feelings of well-being, feelings in which pain signals are obliterated and pleasure signals induced. ”