ーToday I really felt like I'm only able to put forth as much effort into my work as I do resting.
「今日は休むだけ仕事に力を入れれると痛感した一日でした」
to put forth effort で「力を入れる・全力を尽くす」
to really feel like ... で「…と痛感する」と言えます。
ーToday I came to the full realization that if I rest well I can also work well.
「今日はよく休んだら仕事もよくできると痛感した一日でした」
to come to the full realization that ... で「…と痛感する」と表現できます。
ご参考まで!