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.
MDD is a discrete episode of system-wide shutdown — at least five symptoms, at least two weeks, always including depressed mood or loss of pleasure — that changes how a person eats, sleeps, moves, thinks, and values their own life.
A Factory Losing Power
Think of your brain's mood-reward-sleep factory running on three fuel lines: serotonin, norepinephrine, and dopamine. In health, stress comes in (a delivery deadline), the factory ramps up (HPA axis fires), completes the job, then powers down and refuels overnight (sleep resets cortisol). In MDD, all three fuel lines weaken at once — like a brownout — so the factory can't fulfill orders (anhedonia: nothing feels worth making). The night shift breaks (sleep fragmentation). Workers show up but move in slow motion or pace uselessly (psychomotor changes). The manager starts blaming herself for every missed shipment, even old ones (guilt and worthlessness spiral). After weeks of this, the workers wonder if the factory should just shut down permanently (suicidal ideation). The power lines haven't snapped; they're just dimmed everywhere simultaneously.
American Psychiatric Association DSM-5-TR (2022) · NIMH Major Depression fact sheet · FDA black-box warning on antidepressants and suicidality · Rush et al. STARD trial (NEJM 2006) · reviewed 2026-06-01