**Core Concept**
The patient's presentation of sudden hypotension, tachycardia, and black stool in the context of a history of hypertension, coronary artery disease, and medication use suggests a diagnosis related to gastrointestinal bleeding. The key concept here is the adverse effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on the gastrointestinal tract.

**Why the Correct Answer is Right**
The patient's symptoms are likely due to gastrointestinal bleeding, which can be caused by the use of NSAIDs such as aspirin. NSAIDs inhibit the enzyme cyclooxygenase (COX), which is responsible for the production of prostaglandins. Prostaglandins play a crucial role in maintaining the integrity of the gastric mucosa and promoting mucosal blood flow. Inhibition of COX by NSAIDs can lead to gastric mucosal damage, ulceration, and bleeding. The use of aspirin, atenolol, and sorbitrate (isosorbide dinitrate) in this patient increases the risk of gastrointestinal bleeding.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the patient's presentation of sudden hypotension, tachycardia, and black stool.
**Option B:** While coronary artery disease is a risk factor for cardiac arrhythmias, it does not directly explain the patient's gastrointestinal bleeding.
**Option C:** This option is not supported by the patient's history and physical examination findings.

**Clinical Pearl / High-Yield Fact**
Gastrointestinal bleeding is a common complication of NSAID use, and the risk is increased in patients with a history of gastrointestinal disease, older age, and concomitant use of anticoagulant medications.

**Correct Answer:** C. Gastrointestinal bleeding due to NSAID use.