The recognition of uncertainty and thrownness is likely to cause existential anxiety, which is simply characteristic of being. Existential anxiety is normal and healthy if ‘one can accept the responsibility for choice but recognize the potentiality of tragedy’. When existential anxiety cannot be accepted, that anxiety becomes neurotic. Though conceptualized in different ways, neurotic anxiety in general may be understood as a fear of Dasein loss. Some may suffer from a 'stuck’ Dasein, in which the freedom to make decisions is gone; others may feel ontological insecurity, in which they cannot take existence for granted and contrive ways of forcing life to be more 'real’. In addition, neurotic anxiety may also be caused by a perceived inability to understand and interact in the world, what Frankl called 'the existential vacuum’. In these different manners, the 'mentally ill’ inauthentically perceive their world and deny the true possibilities of their Dasein.

Samuel Minier, An “authentic wholeness” synthesis of Jungian and existential analysis

The neurotic who tries to wriggle out of the necessity of living wins nothing and only burdens himself with a constant foretaste of aging and dying, which must appear especially cruel on account of the total emptiness and meaninglessness of his life.

Carl Jung, Symbols of Transformation