Depression sucks. One minute you could be completely fine — and then you just don’t want to try anymore. Or it’s been there for as long as you can remember: a heavy weight on your chest that saps you of all energy.

But what actually causes it? And what can you do about it?

“Depression” actually refers to a cluster of symptoms that can be caused by all kinds of different stuff. Hypothyroidism, Vitamin B12 deficiency, and a few dozen other conditions can all cause depressive symptoms. For this reason, if you’re suffering from depression, it’s always a good idea to see your friendly neighbourhood general practitioner, if only to rule this stuff out.

Still, most cases I’ve come across as a therapist have clear links to what we call “adverse life experiences,” or, as normal people call it, shit that’s happened to you.

The first thing to know is that when it comes to how we, as humans, respond to threats (which is how our nervous systems view adverse life experiences), we have three built-in responses.

The first is our most sophisticated, and it’s pretty unique to humans: talking things out. The second is the less sophisticated fight, flight, or freeze response, which we share with other mammals. And the third is our most primitive response to threat, which even cartilaginous fish use: the shutdown response.

In the face of a threat, we start at the top of the list and work our way down: if social engagement doesn’t resolve it, we move into fight, flight, or freeze. If that doesn’t work, then we shut down. The shutdown response is basically what an animal does when it’s about to be annihilated and has no other option but to numb the pain by disconnecting from the experience.

If, however, our early life experiences were characterized by helplessness — like with child abuse, role reversal with a parent, or loss — then our nervous systems get programmed to respond to present-day stressors by immediately jumping to shutdown.

But what does all this have to do with depression? A hell of a lot, since the exhaustion, hopelessness, loss of pleasure, sleep and appetite issues, and that feeling like you’re moving through soup are exactly what characterize the shutdown response.

Add to this the fact that most people experiencing depression can point to at least one recent adverse life experience, if not a lifetime of them, and we’re onto something important here.

Understanding the shutdown response also explains why Cognitive Behaviour Therapists are always telling you to exercise and socialize, even if you don’t want to: those activities more than most move you out of shutdown mode and back into the more sophisticated parts of your brain. (Eventually.)

And why do other therapists say the therapeutic relationship itself is what heals? Because relating to your therapist lights up the social engagement system, thereby moving you out of shutdown. Cool, right?

All that stuff helps reduce the symptoms, and once those life experiences that programmed your brain to jump right into shutdown mode get resolved by a kickass trauma therapy like eye movement desensitization and reprocessing (EMDR), you won’t need to spend weeks forcing yourself to exercise and talk to people every time something shitty happens.

What all this means is that if you’re experiencing depression, there’s a ton of hope that things can get better. Your brain isn’t broken, it’s just a bit stuck, and a skilled therapist will know just how to unstick it.

John Roche is a therapist in Kitchener-Waterloo.