I'd recommend focusing on your sleep schedule over the next two weeks, especially if you're taking the test in the morning. I'm not a morning person, so I shifted my schedule much earlier starting two weeks before the test. With one week to go, I was adjusted to the new schedule and felt comfortable with it. Also, I'd try and solve problems after you get up in the morning, to get your brain used to thinking at that time (sounds funny, but I found this surprisingly helpful).
That's actually a great piece of advice!
I took a full length GMAT test the day before my actual GMAT and i felt it was very helpful too (getting up in the morning, doing the routine, etc).
If on the last night you are not able to fall asleep a bit longer than usual - that's fairly normal. nobody usually can.
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