(HealthDay News) -- Anemia occurs either when the blood is deficient in red blood cells, or it lacks enough of a protein called hemoglobin.

Some forms of anemia can be life-threatening if not diagnosed and treated, the U.S. Department of Health and Human Services says.

Here's the agency's list of warning signs that you may be anemic:

• Feeling tired and weak.
• Experiencing paleness, dizziness, headache or shortness of breath.
• Having a lower than normal body temperature.
• Having cold or numb hands and feet.
• Having pains in your chest, or a very fast or abnormal heartbeat.
• Feeling irritable.
• Doing poorly at work or school.