私はひどく疲れていた。

English Translation

I was extremely tired.

FYI: ひどく or 酷く is used exclusively in a negative context. 酷い(ひどい)as an adjective means “terrible/awful”.

You can NOT use ひどく/酷く as an adverb in the following positive sentences:

This device is extremely accurate. ==> この機器は非常に正確だ。(このききはひじょうにせいかくだ)

Mary did extremely well in the exam. ==> メアリーは試験の出来がとても良かった。(しけんのできがとてもよかった)