Why Zebras Don't Get Ulcers, and What That Has to Do with PTSD
A zebra runs from a lion. Its heart pounds, its muscles flood with adrenaline, and every system in its body gears up to survive the next few seconds. Then the lion gives up, and the zebra goes back to grazing. Ten minutes later, it looks completely calm.
That image comes from the biologist Robert Sapolsky, who wrote a well-known book called Why Zebras Don't Get Ulcers. His point was simple. Wild animals face real, physical danger, but their stress lasts only as long as the danger does. Once the threat passes, their bodies reset.
People don't work that way, especially people living with PTSD. A memory can trigger the same physical alarm as the original event, even months or years later. It can happen in a grocery store or a quiet bedroom where nothing dangerous is happening.
What the Zebra's Body Does
When a zebra senses danger, its nervous system switches on a set of automatic responses: a faster heart rate, sharper senses, blood pumped toward the legs instead of the stomach. This is the fight or flight response, and it's built to be short.
The zebra doesn't sit around replaying the chase in its head. It doesn't wonder if the lion will come back tomorrow. Once the immediate danger is gone, its brain gets the signal to stand down, and the body follows.
Why the Human Nervous System Gets Stuck
Humans have a capacity zebras don't. We can hold events in mind long after they're over. That's useful for planning ahead, but it comes at a cost after something frightening or overwhelming happens.
In PTSD, the brain's alarm system doesn't get a clear signal that the danger has passed. The amygdala, which flags threat, stays on alert. The hippocampus, which normally files memories by time and place, has a harder time doing that job when an event was overwhelming.
So the body keeps living as though the lion is still nearby. Sleep gets lighter, muscles stay tense, and small surprises land like bigger ones. None of that is a choice. It's what an alarm system does when it hasn't been told to stand down.
Why Small Things Can Set Off a Big Reaction
This is part of why a sound, a smell, or a tone of voice can trigger a full-body stress response years after a traumatic event. The memory isn't stored as a clear story with a beginning and an end. It's stored in pieces, and any one piece can set off the whole alarm.
You may experience hypervigilance, trouble sleeping, or a racing heart in situations that seem ordinary to everyone else. Your nervous system is still bracing for a threat no one has told it is over.
This Isn't a Failure to Move On
A lot of people with PTSD blame themselves for not getting over it the way they think they should have by now. But a body that keeps sounding the alarm long after danger has passed isn't broken. It's doing what it was built to do, aimed at the wrong moment in time.
Treatment for PTSD often works by helping the nervous system finally register that the danger is over. If you've been carrying this kind of alarm for a while, a therapist who specializes in PTSD can help your body learn what your mind already knows: the lion is gone.
If this is landing close to home, you don't have to sort it out on your own. I offer PTSD therapy, and I'd be glad to talk with you.