Never ending wall of depression.

I thought I got this sorted. I thought it was just the job. "Oh it'll go in the summer" I said. Then again I recall that in the winter "oh it's only SAD. It'll be gone by spring" but it hasn't. It's just persistent. 

It's the darkness. It's the cold. It's the feeling that you're facing a 10 foot wall you need to scale. It's there all the time. You're stuck with it morning, afternoon and night. Especially night. Night where it starts to ignite your neurons with thoughts you were adamant not to entertain during the day. Or even thoughts you'd been repressing. Suddenly normal day memories are cast in grey and in regret. And deep lived fears start swimming to the surface. By the morning, you're a wreck. You've been up all night thinking about things that you needn't have bothered with and you're knackered with all the tension and worry you're burdened with. The morning is meant to be a fresh start. "It's always better in the morning" they say. It isn't though. It's like a mental hangover. 

And the usual conversation happens "how did you sleep? What did you dream?" And everyone's fascinated by the weird dreams. But they aren't when it comes to the fact that you didn't sleep. "Just don't think about it" they say. But that's the problem. Thinking. You can't stop. It's like listening to someone talking about breathing and then you can't help think about your breathing. Thinking is an ingrained human attribute.  A skill that's considered higher order. It's not so special when it's undermining you. 

How can you have fun when you're busy thinking of the implications of such. Or suddenly feeling guilty that you're having a good time because somewhere along your own time line you've let someone down, maybe two-three years ago. You can't just let it go. 

Is this a sign of adulthood or is this really depression? Either way, I need help.  I can't cope.