In which of the following situations would paroxysmal symptoms most likely occur?

Paroxysmal symptoms are characterized by episodes that occur suddenly and can be transient in nature. These symptoms often manifest without warning, which is why the answer identifies the occurrence as "suddenly and unexpectedly at any time" as the most accurate representation of when such symptoms typically arise.

This is particularly relevant in the context of certain types of arrhythmias, such as paroxysmal atrial fibrillation or paroxysmal supraventricular tachycardia, which can present with episodes that begin and resolve quickly, often triggered by various factors but not predictable in their onset. Understanding this helps clinicians recognize that these symptoms can occur during various activities or even at rest, but their sudden nature is a defining feature.

The other situations, such as resting, during sleep, or during intense physical activity, suggest contexts that may not typically align with paroxysmal symptom onset. While symptoms can indeed arise during physical activity or rest, they are less characteristically spontaneous compared to the option highlighting their unpredictable occurrence.