It would seem there's a spectrum of them. In a sense all anxiety could be existential in the way it presses on the nerve of one's own particular instance of exi

It would seem there's a spectrum of them. In a sense all anxiety could be existential in the way it presses on the nerve of one's own particular instance of existence. Though I think we'd all describe Neo's awakening in The Matrix as something somewhat more than anxiety. Of course "existential" is a philosophical term. Heidegger, one of the great existential philosophers, famously used the day to day experience of humans in order to access the very nature of being - of existence - because humans are unique in that existence is a fundamental concern for them. Like when Satre writes in detail about the strangeness of door handles, they're something that we use countless times in our day to day lives, we just never notice them until they become a concern for us, like when they break. So an existential crisis is just that feeling of unearthing something fundamental that's always been there, but now has come to the forefront for whatever reason. Personally I believe there is only ever one existential crisis that we go through and whether we face it head on or just the satellites around it, its centre of mass is always that audacious fact that something exists rather than nothing. BTW one doesn't simply answer this question. The resolution of an existential crisis is a new way of life, not merely understanding some standalone empirical fact about psychology or physics.