Some Of These Possible Reasons Why You Feel Tired All The Time Not getting enough sleep Not getting enough sleep can make you feel tired throughout the day. Stress Stress can cause physical and mental exhaustion and feel tired. Poor diet Eating unhealthy foods can lead to low energy and feeling tired. Anemia Anemia is a condition that can cause fatigue and tiredness. Vitamin deficiency Deficiencies in certain vitamins, such as vitamin B12 and iron, can cause fatigue. Dehydration Dehydration can cause fatigue and tiredness. Thyroid problems Tiredness and fatigue can be caused by thyroid problems. Chronic fatigue syndrome Chronic fatigue syndrome is a condition that causes extreme fatigue. Depression Depression can cause feelings of tiredness and fatigue. Medications Some medicines can cause drowsiness and fatigue.