When you fear something that is about to happen your heart beats faster, you breathe heavier. When the thing you fear is a plastic bag over your head this is a real problem. Arielle struggles to breathe. Her fear overwhelms her and she struggles. The little gasps of air she's allowed are not enough to satisfy her.
The ultimate in overwhelming is sexual stimulation. Arielle has a fucking machine in her ass and a vibrator on her clit. She can barely focus on what is happening to her and she has zero choice, but to suffer through.