In my native language, there is an interesting phrase, which is “… as horse”(…成马咧), to describe a very strong emotion.
Usually, it can be used as SLOW AS HORSE when driving speed is not satisfied, or the speed of downloading is horrible, even sometimes horse can run really fast. More often people used this before they take a nap, SLEEPY AS HORSE can certainly describe you feeling.
As a matter of fact, this phrase seemed nothing to do with any horse in the world, simply a easy word to say. Anyway, good luck with HORSE.