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1.
a positive dream about something that no longer exists in reality (a former love etc) and upsets you once you awake.
I don't know if what I have would be considered nightmares, but I often have dreams of reconciling with lost friends/ex significant others that give me such a bubble of happiness and hope, that is horribly burst upon waking up and I end up depressed and mopey for the whole day thinking about how those things will never happen.

Seriously, fuck those kinds of dreams. I shall call them joymares

from: reddit.com/r/AskReddit/comments/xaw3l/if_you_could_get_rid_of_one_vital_bodily_function/c5kqwbf
by kluiez July 28, 2012
 
2.
When you have a dream that makes you go, "Fuck, that was an awesome dream!" until all the implications of that dream actually coming true sink in and you scream in terror.
"Dude, I had the worst joymare about accidentally sending Tom Hiddleston a link to my Tumblr to his Twitter. He tweeted about it. I woke up all stoked until I remembered all the shit I posted about him on my Tumblr."

"I had a joymare that I won $10,000 on a scratch-off lottery ticket, but after I woke up, I remembered I owe my dad $9,000 and would've only gotten $1,000 at best, before taxes. I was fucking pissed!"
by Miss Horrorshow September 19, 2012