Phase 1 · Understand the Body — Why the disease behaves the way it does.
The One-Line Truth
The whole disease in one chain
Everything on this page exists to explain this line.
In fainting (syncope) and orthostatic low blood pressure (hypotension), the bedside team that catches the cluster early — standing blood-pressure check plus careful history plus an ECG — outperforms the team that orders every scan and waits.
The Uphill Water Pump System
Your circulatory system is like a water-pump setup pushing liquid uphill to a hilltop house (your brain). The pump is your heart, the pipes are your blood vessels, and the person controlling the pump's speed and the pipe openings is your autonomic nervous system. When someone stands up, gravity instantly pulls water down into the lower pipes (blood pooling in legs), so pressure at the hilltop (brain) drops fast. Tiny pressure sensors (baroreceptors) in the main pipes detect the drop within one heartbeat and send a signal to the control center (medulla), which immediately tells the pump to speed up and squeezes the lower pipes tighter so water is forced back up the hill. When that system works, water (and oxygen) keep reaching the hilltop. When it breaks — the pump is too slow or irregular, the tank is nearly empty, the squeeze pipes have a leak, or the nerve signals are misrouted — pressure at the hilltop crashes and the house (your consciousness) goes dark.
American Heart Association / American College of Cardiology 2017 Syncope Guideline · European Society of Cardiology 2018 Syncope Guidelines · American College of Emergency Physicians Clinical Policy on Syncope · UpToDate · reviewed 2026-07-07