Imagine your pain signals as tiny ambulances, travelling along the road which is your ascending pain pathway, and your descending pain control pathway as a river, held back by a sluice gate. When released, the river will flow down the hill and flood the road, stopping any traffic from getting through. Close the sluice gate again, and the water will dissipate, allowing the ambulances to resume their journey. So opioids, by releasing the river of descending pain control, can have huge knock-on effects.
