EXCLUSIVE

Halsey claiming an "existential crisis" over the "Black Mirror" episode starring Miley Cyrus, has people connected with the Netflix hit show laughing their asses off ... TMZ has learned.

If nothing else ... Halsey provided some entertainment for 'Mirror' producers when she shared her reaction to the episode about a character named "Ashley O" -- played by Miley. If you missed it, Halsey tweeted, "Black Mirror episode about a pop star named Ashley with colorful hair. Existential crisis: Engage."

She went on to point out her real name is Ashley and joked, "If I die they killed me."

TMZ has seen emails between production execs connected with the much buzzed about episode and they say Ashley O is obviously not based on Halsey. They note that even before shooting the episode ... writers had publicly said they wanted "someone like Miley" to play the character, but never dreamed MC would do it.

In the email chain, one production exec says 'Mirror' co-creator and writer Charlie Brooker was "only vaguely aware" of Halsey. The exec goes on to say, "and if we get asked about it in an interview we'll cheerily confirm that."

Sources connected to the show tell us the Ashley O story was always intended as a metaphor for the careers of young pop stars such as, obviously Miley, but also Britney Spears, Christina Aguilera and even Whitney Houston.

So, as one 'Mirror' exec in the email chain put it, "I think most people can see it's a shameful desperate attempt at self-promotion."

Bottom line, we're told ... Ashley O ain't Halsey, and Halsey ain't Ashley O.