**Core Concept**
Dissociative anaesthesia is a type of anaesthesia that produces a disconnection between the thalamus and the cortex, resulting in a state of analgesia and catalepsy without significant depression of the respiratory or cardiovascular systems. This form of anaesthesia is characterized by a feeling of detachment from the environment and is often associated with a sense of floating or being in a dream-like state.

**Why the Correct Answer is Right**
The correct answer is Ketamine, a phencyclidine (PCP) derivative that acts as an N-methyl-D-aspartate (NMDA) receptor antagonist. By blocking the NMDA receptors in the thalamus, Ketamine prevents the transmission of pain signals to the cortex, resulting in analgesia. Additionally, Ketamine's action on the mesolimbic dopamine pathway contributes to its dissociative and psychedelic effects.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it doesn't specify a drug, making it a vague and unhelpful choice.
* **Option B:** This option is incorrect because it refers to a different class of anaesthetics, specifically inhalational anaesthetics like Halothane, which work by depressing the central nervous system rather than producing dissociation.
* **Option C:** This option is incorrect because it refers to a different type of anaesthesia, specifically spinal anaesthesia, which involves the injection of local anaesthetics into the spinal canal to block pain signals.

**Clinical Pearl / High-Yield Fact**
Ketamine's dissociative effects can be reversed by administering benzodiazepines, such as Midazolam, which can help to alleviate anxiety and promote a sense of normalcy in patients.

**Correct Answer: C. Ketamine**