Encountering the spiritual realm is an intensely overwhelming experience, one that can leave a person completely drained of both physical and mental energy. Confronted by an angelic presence, an individual may be overcome by a profound sense of nothingness and sheer terror, rendering them unable to even hold a basic conversation.
Daniel finds himself in exactly this state, wondering how a mere flesh and blood servant can possibly communicate with a towering spiritual master. The primary approach among commentators is that he views himself as the lowly servant and the angel before him as the lord, completely bewildered by the vast gap between them [רש״י, מצודת דוד, ביאור שטיינזלץ]. Alternatively, another perspective suggests that Daniel is actually distinguishing between two different levels of revelation. In this view, he is speaking to the current angel, who appeared to him in a less intense vision, pleading for this angel to be the one to speak with him instead of the overwhelmingly powerful angel from a previous vision. His fear is that interacting with the greater presence will simply kill him, much like the Israelites at Mount Sinai who begged Moses to speak with them instead of God, fearing they would die [יוסף אבן יחיא].
Even though the angel now appears before him in a human form, the deep anxiety from the initial encounter still grips Daniel, emptying him of all physical strength. He expresses that his power is gone and his breath has completely left him. Since he is actively speaking at that exact moment, this claim of having no breath is understood by some as an exaggeration, meant to illustrate the massive scale of his weakness and panic [מצודת דוד]. However, others see it as an expression of his genuine fear that if the intense revelation continues, his soul will actually be forced to leave his body [יוסף אבן יחיא].