A person who constantly feels blue and really low because of a 'certain' situation (read: an asshole of a lover, political issues, a bad break-up) that made them feel that way. These people are known to constantly weep, think a lot, feel miserable all the time and cry themselves to sleep. Their misery is infectious.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.

Where your kinda depressed or in your feelings but have no reason to be

A distinctive emotional atmosphere generally experienced
1) on Sunday afternoons due to lack of sunlight and a possible hangover.
2) when reading sad and uninspiring literature.

The feeling one gets when he or she has run out of coffee and/or has no means of acquiring a caffeine fix.

A double espresso in a normal-sized coffee mug with a lot of vodka.
Picks you up, gets you alert and SLAMS you down again when the vodka hits.

The fake Spanglish way to say depressed. Makes a depressing sentence become a meme-ish and humorously self-deprecating one.