Anxiety is the whole subject here, and the speaker doesn't treat it as a passing worry. They describe it as something that actively harms them. The poem opens by repeating the word "Anxiety" twice, almost like a person naming an enemy they can't stop thinking about. Then comes the comparison to cyanide, a deadly poison, which makes the feeling sound dangerous rather than merely unpleasant.
What stands out is the sense of slowness. A "slow burn" and a "slow poisoning" suggest that the damage builds up gradually, wearing down the speaker's life bit by bit. Then the imagery shifts: anxiety locks the speaker in a cage and throws away the key, so the feeling is also one of being trapped with no way out.
The final lines return to poison, and anxiety "just wants" to hurt them. That makes it feel almost like a person with a motive. The mood is bleak, tense and helpless, and the short, plain lines make it feel blunt and raw.