You did not calm yourself down. You sat still and watched, and calm turned up. It is worth having that the right way round.

What the research says

A meta-analysis pooling 83 studies found that effortful self control on one task left people worse at controlling themselves on the next, although later work has questioned how large and how reliable that effect really is. Either way, forcing calm out of yourself looks like an expensive way to get it. The size of the effect is genuinely unsettled, so hold the willpower as fuel picture lightly.

Strength of evidence: one line of research. A single study, or a theoretical account.