se me echó la yegüa
(the mare fell over me) •
Used to express that you are all of a sudden tired and don't feel like doing anything else. Also used when, after having agreed on doing something, you suddenly just don't have the motivation to do it.
"Entonces, ¿vamos a ir al cine como planeamos?"
"Oh no, se me echó la yegüa, otro día nomás."
"So, are we going to the movies like we said?"
"Ah, nah, the mare fell over me, maybe another day."