if your head or mind clears, or you clear it, you become free of thoughts that worry or confuse you or the effects of alcohol, a hit on the head, etc. and you are able to think clearly
روشن شدن ذهن, روشن کردن ذهن, خالی کردن ذهن, آرام شدن
As her mind cleared, she remembered what had happened.
I went for a walk to clear my head.