Which of the following is a symptom of overexposure to RF?

Nausea is a recognized symptom of overexposure to radiofrequency (RF) radiation. When individuals are exposed to high levels of RF energy, it can lead to various health effects, one of which is nausea. This can occur due to the body's response to the thermal effects of RF energy, causing discomfort and sickness. In addition, nausea can be associated with the body's stress response, which can be triggered by excessive exposure to RF radiation.

While other options may present symptoms in different contexts, they aren't typically associated with RF overexposure in the same direct way. Hair loss, increased heart rate, and sleepiness can arise from various health issues or environmental factors but do not have a well-defined link to RF exposure specifically. Therefore, nausea stands out as the symptom most directly connected to RF overexposure.