with the fairies

away with the fairies

Seeming eccentric, distracted, or a bit crazy. I can't follow what your mom is talking about—it's like she's away with the fairies all of a sudden.
See also: away, fairy
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

(away) with the fairies

giving the impression of being mad, distracted, or in a dreamworld.
See also: fairy
Farlex Partner Idioms Dictionary © Farlex 2017
See also:
References in classic literature ?
The best proof of this was his caution with the fairies. They were most anxious that he should remain in the Gardens to play to them, and to bring this to pass they tried to trick him into making such a remark as "I wish the grass was not so wet," and some of them danced out of time in the hope that he might cry, "I do wish you would keep time!" Then they would have said that this was his second wish.
ALNWICK Garden will be hoping its latest idea is now "away with the fairies" after creating its very own magical fantasy world.