We keep track of falls. Sometimes it hard to determine exactly what constitutes a fall. For example, if a person slides out of a chair and lands on the ground, is that really a fall?
I asked if anyone had an official definition and, sure enough, they did.
A fall is: Loss of upright position that results in landing on the floor, ground, or an object or furniture, or a sudden, uncontrolled, unintentional, non-purposeful, downward displacement of the body to the floor/ground or hitting another object like a chair or stair; excluding falls resulting from violent blows or other purposeful actions.
A slide out of a chair therefore represents a fall.
I'm still a little confused.