afraid of one’s own shadow 杯弓蛇影；极度胆小；胆小如鼠；草木皆兵

【例句】
What was there to be afraid of you're own shadow?
你到底草木皆兵什么？

Since his house was stolen, a little noise at night will make him feel afraid of he’s own shadow.
自从他家被偷了，晚上有点声响就会让他草木皆兵。