Rozniecki describes the experience of a seizure from the inside, and the horror is that the speaker stays aware throughout. It begins with a knot of fear and a feeling the speaker recognizes, so they close their eyes and pray it's only a dream. Then the sensations "evolve," and control slips away. The speaker stares into nothing, can't speak or move, and looks merely "spaced" to anyone watching.
The central pain is the gap between what's happening inside and what others can see. The speaker screams, but no sound comes out. The repeated "helpless" shows a double isolation: cut off from other people and from their own body. The phrase "trapped in myself" sums it up. The mood is claustrophobic and panicked, and the plain, list-like lines, each ending on a comma, make the fear build without a break. The speaker also fears the state might never end, which makes the final line, "until the seizure finally fades," feel like a gasp of relief rather than a calm resolution.