The speaker admits to a habit of lying: whenever someone asks how they are, they say they're "slammed," meaning busy. The word works as a disguise, because it sounds like an injury and so buys the rest and care the speaker really needs. Then the poem peels the disguise back. Being slammed, for this speaker, means a father's slap during a fight, a little brother saying he wished they were dead, and a mother's words, "So you really don't love us," hitting like a car.
What the speaker feels is hurt, shame, and loneliness. The lie is meant to protect them, but it also keeps friends away, so it isolates them further. The physical details near the end, a swollen face, a blocked nose, a racing heart, make the crying feel raw and close. The mood is confessional and heavy, but also honest: the poem finally says what the word was hiding.