Sort of depends on what you want to say. Realisation comes before knowledge, but after the thing to be realised exists, so you could word these differently. I hadn't realized how starving I was. <-- all past, but starving, then realised - as if telling a story, of the past So if you want to say: present starving, but not realised, you get a little different I hadn't realized how starving I am. - So, in this case, for this present message, the tenses to be "consistent" are not the same. . In your example, you start with "didn't", indicating you are relating a past event. Is this what you intend?

In English you want to keep the verb tense consistent through the sentence. So, these ones: I didn't realize how starving I was. I didn't realize how hungry I was