It's not a major loss of control --not yet-- simply because she doesn't have the brain capacity to warn him beforehand. Still, Clark might seen a faint nimbus (rainbow-like) around her for the next hour or two.

But really, Eirene's pretty much just concentrating on producing the same euphoria in Clark that he's generating inside her; with bucking hips, not-so-quiet noises, and her hands traveling everywhere she can reach.