There isn't a single, universally accepted clinical term for that exact fear, but several concepts come very close, depending on what you mean.

1. Cognitive anxiety (or performance-related cognitive anxiety)
   • This is anxiety centered on the fear that your mind will "freeze" or fail when you need to think or speak.
   • People worry: "I know what I want to say, but what if I can't get it out?"
2. Fear of cognitive failure
   • Used in psychology to describe anxiety about one's thinking processes—forgetting, losing one's train of thought, or being unable to organize thoughts into words or actions.
   • This fear is common in public speaking, exams, and high-pressure situations.
3. Speech anxiety or glossophobia (if it's mainly about speaking)
   • The fear isn't necessarily of the audience itself but of the possibility that your thoughts will disappear or become inexpressible while speaking.
4. Thought blocking
   • This describes the experience of suddenly being unable to continue thinking or speaking, rather than the fear of it.
   • Someone may fear that thought blocking will occur during conversation or a presentation.
5. Executive dysfunction (more a cognitive phenomenon than a fear)
   • If the concern is about translating intentions into actions ("I know exactly what I want to do but can't initiate it"), this relates to executive functioning.
   • The accompanying anxiety can become a fear that one's thoughts won't become actions.

Philosophically

What you're describing also resembles something existential philosophers discussed. Kierkegaard, whom you've been reading, often wrote about the gap between possibility and actuality. One source of anxiety is the fear that one's inner life—ideas, intentions, aspirations—may never become concrete action. It's not merely fear of failure but fear that the self cannot fully express itself in the world.

If you mean something very specific...

If you mean:

• "I know what I think, but I'm afraid I won't be able to say it." → fear of cognitive failure, speech anxiety, or fear of thought blocking.
• "I'm afraid my intentions won't become actions." → this can relate to executive functioning, action paralysis, or performance anxiety.
• "I'm afraid my inner experience is fundamentally incommunicable." → philosophers sometimes discuss this as the problem of the ineffability of experience—the limits of language in expressing thought.

So while there isn't a single diagnostic label like "glossophobia" for this exact fear, "fear of cognitive failure" is probably the closest psychological description, and anxiety about the gap between thought and expression is a good philosophical description. It's a concern that many writers, speakers, and thinkers have expressed: the fear that the richness of one's mind will fail to survive the journey into words or deeds.

What you're describing sits at the intersection of existential philosophy, phenomenology, and philosophy of language. It's a richer and more fundamental anxiety than ordinary performance anxiety.

There are a few traditions that illuminate it.

Kierkegaard: possibility becoming actuality

Your formulation is very Kierkegaardian. For Kierkegaard, the self is not a static thing but a relation that must become itself. Anxiety arises because we live between what we could become (possibility) and what we actually become (actuality).

Your fear isn't simply, "What if I fail?"

It's closer to:

What if my inward life never succeeds in becoming outward reality?

The anxiety is that one's authentic self remains trapped in possibility—never adequately embodied in speech, work, relationships, or action.

Wittgenstein: the limits of language

Wittgenstein approached the problem differently.

His famous line,

"The limits of my language mean the limits of my world,"

is often interpreted as suggesting that language shapes what can be expressed and even thought. Some aspects of experience resist articulation. At the end of the Tractatus, he concludes:

"Whereof one cannot speak, thereof one must be silent."

He doesn't mean such things are unimportant. Rather, some dimensions of life—ethics, aesthetics, the feeling of existence itself—cannot be fully captured in propositions.

Phenomenology: lived experience exceeds description

Phenomenologists such as Maurice Merleau-Ponty argued that lived experience is always richer than any description of it.

Language doesn't simply transfer thoughts from one mind to another like copying a file. It gestures, approximates, evokes. There is always a remainder.

In that sense, the fear that your experience cannot be perfectly communicated is not irrational—it reflects a genuine feature of human existence.

Rilke: the pressure to make the invisible visible

The poet Rainer Maria Rilke often returned to this tension.

His poems suggest that art is the attempt to give outward form to an inner reality that can never be fully objectified. Every poem succeeds and fails simultaneously: it reveals something, yet always leaves something unsaid.

What kind of anxiety is this?

If I had to give it a philosophical name, I'd call it the anxiety of expression or the anxiety of incarnation.

"Incarnation" here isn't necessarily religious. It means making something inward become embodied—giving thought a voice, intention an action, imagination a form.

The fear is not merely that others won't understand you.

It's that:

• your thoughts are finer than your words,
• your intentions are larger than your actions,
• your self exceeds every expression of it.

Is the fear justified?

In one sense, yes.

No sentence captures a thought perfectly. No painting exhausts the artist's vision. No action completely expresses a person's character. There is always a gap between inner life and outer manifestation.

But that gap may not be a defect—it may be constitutive of being human.

The philosopher Martin Heidegger suggested that truth is not the perfect correspondence between an inner idea and an outer statement. Rather, truth is a gradual unconcealing. We reveal ourselves only partially, over time, through speech, action, and relationships.

Seen this way, expression is less like transferring information and more like participating in an ongoing disclosure of who we are.

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Your question also reminds me of something the philosopher William James observed: our stream of consciousness is continuous, fluid, and richly textured, whereas language is discrete and sequential. We must flatten a multidimensional inner life into a line of words. Some loss is inevitable.

Perhaps the deepest existential move is not to eliminate that loss but to accept it. The goal is no longer to achieve perfect expression—which may be impossible—but to allow one's possibilities to become actual imperfectly. Every sincere conversation, every essay, every act is an approximation. The self is not fully translated into the world in a single moment; it is expressed incrementally, always with a residue that remains unspoken. That residue is not necessarily evidence of failure. It may simply be the measure of how much richer consciousness is than any one of its expressions.