(HealthDay News) -- About 15 of every 100 adults suffer from depression, according to AARP.

Depression is more than just a case of the blues. AARP offers this list of common warning signs:

• Difficulty concentrating, problems with memory, and difficulty making decisions.
• Becoming irritable, angry, worried, agitated, anxious, pessimistic, or indifferent.
• Over an extended period, being sad or unexplained bouts of crying.
• Changes in sleep habits, as well as appetite.
• Loss of interest in activities you once enjoyed.
• Feelings of hopelessness.
• Unexplained aches and pains.