Wiktionary
n. (context existentialism English) A state of panic or feeling of intense psychological discomfort about questions of existence.
Wikipedia
An existential crisis is a moment at which an individual questions the very foundations of their life: whether this life has any meaning, purpose, or value. This issue of the meaning and purpose of existence is the topic of the philosophical school of existentialism.
Usage examples of "existential crisis".
It's right then I locked myself in the bathroom and had what the psychology textbooks would call a quickie existential crisis.
The end of adolescence is the perfect age for an existential crisis, don't you think?
Deflecting his existential crisis for a moment, Hamlet turns the plot on the plotters, substituting their names for his in the death warrant they carry from King Claudius.
You see, I'm going through a bit of an existential crisis and I need her advice.
Christ almighty, he thought, she's having a goddamned existential crisis.