Why can't I just snap out of it?

Is this depression, or am I just being lazy, dramatic, or weak?

Depression is not a lack of willpower. It affects motivation, energy, concentration and sleep at a biological and psychological level. It isn't something you can out-effort your way through, any more than you could think your way out of a broken leg. If you've stopped enjoying things you used to, find basic tasks exhausting, or feel flat, numb, or hopeless for weeks at a time, that's depression doing what depression does, not a personal failing.

Why do I feel this way when nothing "bad" is happening in my life?

Depression doesn't require a visible trigger. It can build slowly from accumulated stress, unprocessed grief or trauma, burnout, hormonal or health factors, or patterns of thinking that formed a long time ago, sometimes with no single identifiable cause at all. Needing a "good enough reason" to feel this low is one of the most common and unhelpful pressures people put on themselves.

Will therapy actually help, or will I just be talking about how bad things are?

Talking about how bad things are is usually part of it, especially early on, but the point isn't to sit in it indefinitely. Good support helps you understand what's maintaining the low mood, works gently to rebuild motivation and structure without pressuring you, and addresses whatever's underneath it, whether that's grief, trauma, burnout, or something else. It's slower than a quick fix, but it aims at something more lasting than temporary relief.

What if I don't even know why I feel like this?

That's genuinely common, and not a barrier to starting. Part of the work is exploring that together rather than expecting you to arrive with a diagnosis or a tidy explanation already worked out.

How do I know if it's "serious enough" to seek support?

If low mood has lasted more than a couple of weeks, is affecting your sleep, appetite, work, or relationships, or you've noticed yourself withdrawing from people and things you used to care about, that's enough reason on its own. You don't need to wait until it feels unbearable.