Everyone feels sad or “blue” from time to time for a few days or weeks. Depression is when these feelings don't go away and they interfere with daily life. Depression is a real illness. It makes you feel sad and helpless. It gets in the way of your life and relationships. It inhibits your ability to think and act. But, with help, you can feel better again.
Brain chemicals affect your body as well as your mood. So depression may do more than just make you feel low. You may also feel bad physically. Depression can:
Cause trouble with mental tasks such as remembering, concentrating, or making decisions
Make you feel nervous and jumpy
Cause trouble sleeping. Or you may sleep too much
Change your appetite
Cause headaches, stomachaches, or other aches and pains
Drain your body of energy
It is common for people who have chronic health problems to also have depression. It can often be hard to tell which one caused the other. A person might become depressed after finding out they have a health problem. But some studies suggest being depressed may make certain health problems more likely. And some depressed people stop taking care of themselves. This may make them more likely to get sick.