In "Hypno's Naptime", after the children are returned to normal, one of the club members explains why they where able to 'unhypnotize' everyone. During this speech, he says "Sleep emits dream waves." Shouldn't that be Drowzee? Turns out that particular word didn't get translated. Drowzee's Japanese name is Sleep!
No, they didn't mean sleep emits dream waves. Earlier on they said something to the effect that Drowzee emits dream waves. The man was explaining why Drowzee canceled out Hypno's hypnosis. It is a slip-up.