In certain circumstances, which may include seeing blood or having your eyes examined, your involuntary nervous system behaves as if you were lying down, when actually you are sitting or standing up.
* ويُظن انه خلل يصيب احد اجهزة الجسم الذي يُفترض ان ينظِّم جريان الدم ،‏ كما يحصل مثلا عندما تقف بعد ان تكون جالسا .‏