“镇静状态”常见的英文表达可以是 “a state of calmness” 或 “a calm state” 。
“calmness”意思是“平静；镇静”，“a state of...”表示“……的一种状态”；“calm”本身就有“平静的；镇静的”意思，“a calm state”即“一种平静/镇静的状态”。
例如：
After the initial shock, she gradually entered a state of calmness.（最初的震惊过后，她逐渐进入了镇静状态。）
He managed to maintain a calm state during the emergency.（在紧急情况下，他设法保持了镇静状态。 ）