Which of the following is a sign of a stroke?

Sudden balance loss is indeed a critical sign of a stroke. Strokes can disrupt blood flow to the brain, which may lead to sudden difficulties with coordination and balance. Other symptoms often accompany this, such as confusion, trouble speaking, or one-sided weakness. Recognizing sudden changes in a person's ability to balance can be vital for timely medical intervention, which can significantly improve outcomes.

On the other hand, rapid heart rate, persistent cough, and fever are not specific indicators of a stroke. These symptoms could arise from various other medical conditions and do not directly relate to the acute neurological issues presented in stroke cases. Thus, understanding the specific manifestations of a stroke is crucial for providing effective care and ensuring prompt medical assistance.