**Core Concept**
Acute complications of Protein-Energy Malnutrition (PEM) can arise due to the body's inability to maintain homeostasis in the face of severe energy and protein deficiencies. These complications often involve electrolyte imbalances, metabolic derangements, and immune system dysregulation.

**Why the Correct Answer is Right**
The most common acute complication of PEM is hypoglycemia, which occurs due to the depletion of glycogen stores and impaired gluconeogenesis. The liver's ability to convert stored glycogen into glucose is severely compromised, leading to low blood glucose levels. This can be exacerbated by the body's increased reliance on glucose for energy during periods of PEM.

**Why Each Wrong Option is Incorrect**
* **Option A:** Hypothermia is not a direct acute complication of PEM, although it can occur in severely malnourished individuals due to impaired thermoregulation.
* **Option C:** Hypokalemia is not typically associated with PEM, as potassium levels are often elevated in the setting of malnutrition due to impaired renal function.
* **Option D:** Hypermagnesaemia is not a common complication of PEM, as magnesium levels are often decreased in malnourished individuals due to impaired absorption and increased urinary excretion.
* **Option E:** Eosinophilia is not a direct acute complication of PEM, although it can occur in response to various stressors, including malnutrition.

**Clinical Pearl / High-Yield Fact**
In the setting of PEM, it's essential to prioritize the restoration of normal glucose levels to prevent further complications, including seizures, confusion, and even death.

**Correct Answer: B. Hypoglycemia**