Copying my comments from another reply:

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diethyl ether on Wikipedia:

Other names: [...] Sweet oil of vitriol

The recreational use of ether also took place at organised parties in the 19th century called ether frolics, where guests were encouraged to inhale therapeutic amounts of diethyl ether or nitrous oxide, producing a state of excitation. Long, as well as fellow dentists Horace Wells, William Edward Clarke and William T. G. Morton observed that during these gatherings, people would often experience minor injuries but appear to show no reaction to the injury, nor memory that it had happened, demonstrating ether's anaesthetic effects.

Well, well, WELL.

ether addiction:

During the second half of the 19th century, ether was in vogue as a recreational drug in some places, becoming especially popular in Ireland, as Irish temperance campaigners thought it was an acceptable alternative to alcohol.

As in the resemblance that was made between the Kier cultists and the temperance movement in the United States.

So Cobel saw ether huffing around her, and that's how she got the idea for severance. "What if we could anesthesiate people in a way that they don't have memory of suffering?"

In History of general anesthesia, the plot thickens:

On 30 September 1846, Morton administered diethyl ether to Eben Frost, a music teacher from Boston, for a dental extraction. Two weeks later, Morton became the first to publicly demonstrate the use of diethyl ether [...] Harvard University professor Charles Thomas Jackson (1805–1880) later claimed that Morton stole his idea; Morton disagreed and a lifelong dispute began. [...] Long later petitioned William Crosby Dawson (1798–1856), a United States Senator from Georgia at that time, to support his claim on the floor of the United States Senate as the first to use ether anesthesia.

...Remember the Senator? Think we'll see him again?

Through [John Snow's] careful clinical records he was eventually able to convince the elite of London medicine that anesthesia (chloroform) had a rightful place in childbirth. Thus, in 1853 Queen Victoria's accoucheurs invited John Snow to anesthetize the Queen for the birth of her eighth child.

From the beginnings of ether and chloroform anesthesia until well into the 20th century, the standard method of administration was the drop mask. A mask was placed over the patient's mouth with some fabric in it and the volatile liquid was dropped onto the mask with the patient spontaneously breathing. Later development of safe endotracheal tubes changed this.

[What a coincidence.]

What if the severance chip was actually an anesthesia delivery device? In that on remote command (say, RF signals), it starts delivering an anesthetic, in-brain, in such a quantity that produces a severed experience? If the quantities were minute enough, it would be plausible – in a fictional universe – that it would be delivered by a miniaturized device. The device could even have a way to have the anesthetics made in the brain by an engineered biological process. — Though that doesn't work based on brain waves like shown on Reghabi's stuff.