Medically, anaesthesia is a "balanced triad" of three elements: analgesia (pain relief), narcosis (sleepiness), and muscle relaxation. It's a spectrum: we talk about having various "planes" of anaesthesia that are in principle relatively woolily defined but in practice oddly specific. An example would be the difference between a "light" form of general anaesthesia for a relatively non-invasive procedure -- such as a broncoscopy, which can be performed under heavy sedation; and something where unexpected movement can have catastrophic effects, such as surgery on the spine. It is rare, but not terribly so, for some surgical stimuli to cause local responses or motion, even when the patient is "completely under", ignoring local reflex arcs which may (or may not!) be affected by the anaesthetic agent.

A good, modern anaesthetist in a western hospital has access to an incredible array of information about their patient, ranging from their complete physiological state to the partial pressures of anaesthetic gasses going into, and out of, their lungs (and thus in their blood stream). This largely means that the horror stories of the past about people "waking up and being unable to move" -- the triad becoming unbalanced and muscle relaxation ± analgesia being (barely) adequate, but narcosis clearly not -- remain in the past.

I've probably waffled incoherently enough, but it's worth reiterating that anaesthesia is a _field of medicine_ in its own right. There are literally thousands of approaches, drug combinations, and "gotchas" to deal with, in all sorts of situations -- right the way from the straightforward and simple to patients with massive facial injuries where it is very difficult to know how to intubate them without causing further damage. Drug combinations are prescribed on the basis of the patient, the indication, and local rules and availability (including toxicity to the operator and cost -- many anaesthetic gasses are carcinogenic if you're exposed to them for a long period of time in trace amounts, which occasionally becomes an issue).

Re: the content of this article --- if you have blood in your stool, see your doctor. (S)he won't be embarrassed about shoving a finger up your arse, and the outcomes range from "eat more fruit", or "don't have anal sex for a little while" to lifesaving surgery.

Thanks, that's very interesting! And yes, I definitely agree about seeing your doctor. We're often unreasonably embarrassed about things like this, but a good doctor will have no problems putting people at ease. And obviously the outcome can be really bad if something serious goes undetected.