I definitely think something is wrong in the sentence. That would be why it is not clear to you... It is not written correctly! It is not clear at all, not just to you : ) Your sentence sounds a lot better than the original! I will touch it up a little: "Since we hadn't slept much, we didn't have enough/much energy"

In my opinion , you use too many words to express a simple notion . Perhaps , you are making a sentence with Chinese thinking As we did not have good sleep , so we were not energetic ==OR Given that we did not sleep well , we did not have enough energy