Many people have been found being unknown to what exactly is depression?
How do you know you're in depression?
Honestly, there is no specific answer.
But here is my attempt to clear it out a bit.
Self-aware individuals diagnosed with depression seem to have many threads of commonality to tie together their personalities. They may typically feel excess amounts of guilt, constantly sensing that they are a constant hindrance to their companions. They are desperate for validation and affection, yet afraid and avoidant of forming mutual dependencies. They are acutely aware of how ridiculous their disease makes them seem, and how irrational they act and are during the troughs of their life.
If you find something like this happening to you.
I would suggest, visit a psychiatrist or you could even just be frank about it and talk to your freinds (or whoever is closest to you) about it.
In depression or not. What's trouble's you needs a healthy way out. If not given a way, it can turn into depression.