There's apparently a thing called the "fentanyl fold," when a user bends over, but supposedly it isn't exclusive to fent.
https://archive.ph/FbFDM

Dr. Daniel Ciccarone, UCSF professor of addiction medicine, said what he calls the “nod” is a common side effect of opioid use.
“It’s not much different than the experience of being in a boring lecture and falling asleep,” Ciccarone said. “It’s a version of losing consciousness. But not to the point of losing consciousness –– they’re still conscious.”
These nods have always happened to varying degrees with other opioids, particularly heroin. The nods with fentanyl, however, seem to be more extreme, Ciccarone noted. And it’s often a sign that a person has taken too strong a dose, he said.
“What you’re witnessing is the balance point between passing out –– when you lose all muscular control and are on the floor –– versus some small remnant of consciousness that is keeping the person upright,” he said.
Fentanyl, which can be up to 50 times more potent than heroin, can induce this “low point of consciousness,” which is believed to be euphoric, Ciccarone said.
“As opioids get stronger, the nod gets deeper,” he said. “The dials are just being turned down. Consciousness, breathing, muscular control are going down … and this is just one of the visible signs of it.”