I said in my post on JLPT D-3 that the dice were cast. Well, it’s not entirely true. Concerning the vocabulary and grammar part, I indeed think that you won’t change your result with some last minute exhausting cramming. Vocabulary and grammar are only a matter of what you know. But the reading part and the listening part are a matter of what you know + your capacity to concentrate. This means that, for those parts, your performance on the day of the test is almost as important as your knowledge. It is no use to know 6000 words if you can’t concentrate on what you are reading. When I study the reading part, I sometimes can’t figure out what the text is about, it just doesn’t make sense, even if I know almost all the words of the text. That’s just because I am not concentrating on the text, either because I am tired or because I keep thinking of the remaining time and try to read as quickly as possible. Same for listening. I let my mind fly away and all of the sudden I realise that I wasn’t listening at all! But there is no second chance as the audio is played only once.
That’s why I recommend to practice some sport, or even just go for a walk, take some fresh air, eat well and sleep well!