how do you know if you're depressed?

healthy 19 yo male

last couple days i've been watching a bunch of tv shows (netflix), sounds strange but I watch a bunch of drama shows and during romance scenes I start getting caught in my own thoughts about loneliness, not doing what I really wanna be doing in life, Ive basically had the heart in the stomach feeling for the last like 3 days and have no motivation to even go to the gym anymore and get super pissed at super small things. main question is, is this something that'll pass? something more serious? I dont have the feeling of just wanting to lay in bed all day and cry or anything like that.