I periodically suffer from what assume are symptoms of depression, but I can usually pinpoint the triggers that caused them (a lengthy social media session filled with large amounts of scrolling reviewing dozens of happy families hugging and kissing each other, a missed deadline that I'm emotionally connected to, a hangover, rainy weather, etc.)

Although I don't do this every time I suffer from the symptoms, usually a high intensity workout of some sort (a relatively fast 2 to 3 mile (or further) run, 45-60 min lifting session of fast paced lifts with super sets, etc.) will almost instantly "cure" my symptoms.

I can probably do some research or go see a doctor to confirm whether what I experience is anything potentially connected to depression, but I just haven't been motivated to and again, can usually fix what I'm feeling with a workout. Not really sure how to proceed, if at all...

One of my friends went to a psychiatrist for ADHD symptoms and he got diagnosed with depression. He was like, “I didn’t know I was depressed!”

That's usually a yes, or at least "keep watch". There's grades of it, things like cyclothymia and disthymia, too.