Tomorrow is World Mental Health Day (as well as Depression Screening Day), a time when experts all over the world try to raise awareness about mental health issues.

This year, the day is focused in particular on the mental health of older adults. According to the World Health Organization, 15% of people over age 60 suffer from a mental disorder. In the U.S., the highest rates of suicide are in middle aged and older adults. (Here are 7 ways to help older people who are depressed.)

In this video, Kenneth Robbins, MD, psychiatrist, University of Wisconsin-Madison, notes that some people with depression may not be able to talk about it. “Some people can't really tell you that they feel depressed because they're not quite aware what that feeling is,” he says.

“In diagnosing depression, one of those two things has to be present,” says Dr. Robbins. “Either somebody has been unhappy and sad consistently over at least a couple of weeks and often for longer than that. Or, over that same couple of weeks, they say that there's nothing that they've been able to enjoy.”

To find a free screening site near you, or to take a screening test online, go to HelpYourselfHelpOthers.org.