If you have lost your appetite for a few days without any other symptoms, it could be due to various reasons like constipation, anxiety, medication side effects, or even stress. It is recommended to eat more frequently, consume high-energy meals, and consider meal replacement products if needed. If you continue to eat very little for 5 days or experience significant weight loss, it is important to consult a doctor. Additionally, if you develop extreme fatigue, difficulty concentrating, or persistent nausea/vomiting, it is best to seek medical advice.