Discouragement
Despondency, Dejection, Disappointment
noun, verbal noun
Your guts feel like they're falling when you experience a lot of discouragement. You know that sinking feeling you get in the pit of your stomach? That's your guts falling!
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
息子は、受験に失敗して落胆しているんだ。
My son failed an exam and is discouraged.