The only factor I would consider is that I gave my last GMAT Prep mock the night before, from 9 pm to 1:30 am but I couldn't fall asleep in any case. I did feel a teeny bit fatigued towards the end of the test but that doesn't justify a 5 point drop in verbal.
How do you feel you did in the last 5-8 questions? The problem is if you do poorly in that part of the test there is no time to recover. If you miss problems near the beginning or middle than you still have the rest of the test to improve your score. Doing poorly at the end of the test can really hurt your score. Lets say someone had a v37 going into the last three problems. Getting them wrong could move then down to v35 versus if they got them right it could move them up to v40. You're almost there
You might be right. My mind blanked out on the last 2-3 questions but I didn't expect it to bring me down 5 verbal points.