It starts out slow.
Those occasional bad moods and torpid mornings, the flashes of irritability, they grow, they lengthen. That’s how it starts. The hollowness inside grows and festers until it swallows everything, you can’t remember what joy is, you can’t remember what being happy feels like. Getting out of bed takes fantastic effort, smiling kills you a little more inside every time.
Eventually, all the pent up emotions seep out of the cracks of that hollow state; this manifests itself differently depending on the person.