고 지치다

be worn out and exhausted

지치다 is being worn out — drained rather than merely sleepy. -고 chains it to another state word, and in four of these eight lines that word is 힘들다 'be tough': 정신적으로 힘들고 지쳤을 때 쓰는 표현이에요 'it's the expression for when you're mentally worn down'. Repeating it, 지치고 지쳤는데, means utterly spent.

Register: casual; about fatigue