Which of the following symptoms could suggest the presence of diabetes?

Excessive fatigue is a common symptom that may indicate the presence of diabetes. When blood sugar levels are not properly regulated, either due to insufficient insulin production or insulin resistance, the body's ability to use glucose for energy is impaired. This can result in a lack of energy, leading to feelings of fatigue and weakness.

In contrast, increased energy levels, skin clearing, and improved vision are not typically associated with diabetes. Increased energy levels would suggest good metabolic control, while skin clearing could be a result of various factors unrelated to diabetes. Improved vision might occur temporarily in some cases of fluctuating blood sugar levels, but it does not align with the chronic symptoms often seen in uncontrolled diabetes. Thus, excessive fatigue stands out as a significant warning sign of potential diabetes.