She didn't trip or feel faint, and she gets up immediately on her own after hitting the ground. I'm wondering if this could be a neurological problem. She's very healthy for her age and is not on any medication, even aspirin. She gets regular checkups with good blood pressure and sugar and cholesterol levels. This general term encompasses situations such as you describe in which a person suddenly finds themselves down with no warning.
Drop attacks are very serious.
They can result in death if they occur at a moment when unconsciousness is not a good idea, such as when a person is driving, climbing stairs, or crossing the street. Nonetheless, drop attacks are usually preventable if a correct diagnosis is made. There are three principal causes of drop attacks. The first is heart block, in which the heart beats arrhythmically instead of maintaining its metronomelike regularity. In either case, the heart's pumping ability is markedly compromised and a drop attack is a predictable result.