Used mostly in anime and manga, the term growing mushrooms refers to when a character has become immensely depressed or saddened. The character is often shown to literally grow mushrooms on their body, signifying that their soul is, for the time being, in a dark and dank place. (Mostly occurs with more dramatic and over the top characters who can't stop crying every 2 seconds 😒)
Senpai: (crying because the girl of his dreams thinks he's dramatic and egocentric)
Girl: "Senpai, quit growing mushrooms around me; the smell is absolutely noxious!"
The feeling of childhood freedoms slipping away without any warning, the loss of unstructured time for relaxation, the necessity to work to survive. The impending journey across space and time to achieve one's dream, the feeling of hopelessness when that dream is not achieved, reflection upon one's carefree childhood, longing, regret and desire for a good retirement fund and a glass o' prune juice.
My Dad paid off the mortgage with my college fund, because since I'm "growing up", I should learn to pay for my own things.