expression
to make matters worse; what's worse
Fixed expression used to introduce an additional negative point, often at the beginning of a sentence.
財布を落とした。さらに困ったことに、携帯の電池も切れていた。
I lost my wallet. To make matters worse, my phone battery was dead.
雨が降り出した。さらに困ったことに、傘を持っていなかった。
It started raining. What's worse, I didn't have an umbrella.
Phrase composed of さらに (furthermore) + 困った (troublesome, from 困る) + ことに (adverbial form of こと, 'thing'). Literally 'to a further troublesome thing'.