**Core Concept**
The patient's presentation with altered sensorium, hypotension, and wide QRS complexes on ECG is suggestive of a severe anticholinergic toxicity, likely secondary to tricyclic antidepressant (TCA) overdose. Anticholinergic toxicity can lead to central nervous system (CNS) depression, cardiac dysrhythmias, and hypotension due to the blockade of nicotinic and muscarinic receptors.

**Why the Correct Answer is Right**
The next best step in managing this patient is to administer physostigmine, a cholinesterase inhibitor that can cross the blood-brain barrier and reverse the anticholinergic effects. Physostigmine works by increasing the concentration of acetylcholine in the synaptic cleft, thereby overcoming the blockade of nicotinic and muscarinic receptors caused by TCAs. This can help improve CNS function, cardiac conduction, and blood pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** Activated charcoal administration is not the next best step in this scenario, as it is more effective when given within 1 hour of ingestion and may not be effective in reversing the already established anticholinergic effects.

**Option B:** Gastric lavage is not recommended in this case, as it can cause more harm than benefit, especially in a patient with altered sensorium and hypotension.

**Option C:** Cardiac monitoring and supportive care are essential in managing TCA overdose, but administering a beta-blocker like propranolol would be inappropriate, as it can worsen the cardiac effects of TCAs.

**Clinical Pearl / High-Yield Fact**
In patients with TCA overdose, remember the "rule of 5": a QRS duration of > 100 ms, a heart rate of 300 ms are associated with a high risk of cardiac complications.

**Correct Answer:** D. Physostigmine administration is the next best step in managing this patient.