Once at a rank test, I saw an adult student pass out. She was out cold before she hit the mat. And because she had collapsed from a standing position and was unable to catch herself, she hit hard. The good news: The mat cushioned the impact. The bad news: She still suffered a mild concussion.
This student had diabetes. Although she had eaten about three hours before the test, her anxiety and stress resulted in an adrenalin rush. This caused her blood sugar to drop. Consequently, she lost consciousness.