Lethargy During Fasting: Normal or a Sign of Dangerous Dehydration? Doctor Explains

Feeling weak during fasting is often considered normal, but in certain conditions it can be a sign of dangerous dehydration that should not be ignored. Dr. Ihsanul Rajasa, Sp.PD, FISQua, Internal Medicine Specialist at RS Pondok Indah Bintaro Jaya, explained that not every feeling of weakness during fasting indicates a serious condition. ‘Feeling weak during fasting often occurs as the body adapts to changes in eating patterns and fluid intake. However, not all feelings of weakness are the same,’ Dr. Ihsanul said in an exclusive interview with Kompas.com, on Wednesday, 25 February 2026. The symptoms include weakness that is still tolerable, light dizziness that improves after rest, and reduced concentration but still able to carry out activities. This condition generally improves as the time to break the fast approaches and is not accompanied by significant impairment of bodily functions. This can occur during fasting if fluid intake during sahur is not sufficient or daytime activity is too high. Symptoms of mild to moderate dehydration include:

“If there are dangerous symptoms, the fast should be stopped and fluids should be given immediately. If it does not improve quickly, seek medical help promptly,” Dr. Ihsanul emphasised. “The duration of fasting around 12–14 hours generally does not cause severe dehydration in healthy people.” “However, recognising signs of fluid deficiency early helps prevent the condition from worsening.” “Mild weakness during fasting remains a normal bodily response.” “Weakness accompanied by little or very dark urine, severe dizziness, or impaired consciousness should be watched closely.” “Recognising the difference helps determine when fasting is safe to continue and when it must be stopped for safety.”