nodstopper
noun
A sudden memory that jolts one to full consciousness due to possibly requiring action.
As Gerda gently drifted toward sleep, her mind wandered from the date she’d had that evening, to the scene with the locksmith in the movie they’d watched together, to the realization that she’d left her own front door unlocked. The nodstopper bolted her awake, and she got out of bed to go lock her door.