sleep talking; somniloquy
Refers to the act of talking while asleep, or the words spoken during sleep.
He often talks in his sleep.
Last night I heard sleep talking from the next room.
noun, noun which may take the genitive case particle 'no'
Figurative use: something as meaningless or absurd as words spoken in sleep. Often used dismissively.
That plan is not even worth calling nonsense.
His excuse is complete gibberish.
Stop spouting nonsense like that and make a proper plan.
His proposal sounded like absolute nonsense, and no one took it seriously.
寝言 literally means talking in one's sleep and is used figuratively for nonsense someone says while seemingly not thinking straight, while 戯言 refers to foolish talk in general without that sleep-related image.