Both of them are correct grammatically but I myself tend to use that a lot. It depends on you but if i were you, i'd omit the first that in the first sentence, like this : "It means you are so tired that you can't stay awake any longer" Good luck ;)

The first sentence is more accurate. Its structure is used in actual conversation, so you'd better apply it to real life just to make your talk with people more ambiance.

Thumbs up....Surely you've made a correct sentence... if you haven't advanced in your sentence structure.. i'll strongly suggest that you keep your sentences to a easy and rather simple structure.. because using complex structure can confuse you even more. Good luck

i think the second one is better