**Core Concept**
Postoperative generalized convulsions can be caused by various factors, including electrolyte imbalances, hypoxia, and anesthetic effects. The underlying principle being tested here is the identification of a specific cause of postoperative seizures.

**Why the Correct Answer is Right**
The correct answer is likely related to the anesthetic effect of a specific medication. Postoperative seizures can occur due to the withdrawal of benzodiazepines or barbiturates, which are used to induce anesthesia. When these medications wear off, there can be a rebound effect leading to seizures. This is particularly true for benzodiazepines, which have a high potential for dependence and withdrawal seizures.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because electrolyte imbalances, such as hypo- or hypernatremia, can cause seizures, but they are not the most likely cause in this specific scenario.

**Option B:** This option is incorrect because hypoxia can cause seizures, but it is not the most direct cause of postoperative seizures in this context.

**Option C:** This option is incorrect because anesthetic agents, such as propofol or isoflurane, can cause seizures, but they are not the most likely cause in this specific scenario.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that benzodiazepine withdrawal can cause seizures, especially in patients who have been taking high doses or for extended periods. This is a critical consideration in the postoperative period, especially in patients who have been receiving benzodiazepines for sedation or anesthesia.

**Correct Answer:** D. Benzodiazepine withdrawal.