More than 70 percent had witnessed violence and more than half had become victims of violence, often torture, themselves, said the chamber's president Dietrich Munz.
"At least half of the refugees have a psychological illness," Munz told a Berlin press conference, citing empirical studies from recent years, before the recent surge in refugee arrivals.
Most common were post-traumatic stress disorder and depression, sometimes so severe that patients are suicidal.
Forty per cent of refugee children had witnessed violence, and "26 percent had to watch family members being attacked", said the professional body.
More than 40 percent of adult refugees have nightmares, and 50 percent have flashbacks where they relive a traumatic event "as if it were really happening again", Munz said.
Many refugees suffer from heightened noise sensitivity, jumpiness and insomnia, as well an inability to cope with confined or crowded spaces, said the chamber.
Most are treated with medication that tackles symptoms but not root causes, Munz said, calling for better mental health care for refugees.
At the moment, 3,000-4,000 psychotherapies a year were being offered to refugees in Germany, Munz said, estimating that demand may be 20 times higher.