If it was a bubbling error and not a reasoning error, you shouldn't be dismayed.I remember before the second diagnostic I had two hours of sleep. By the last section, I was mentally exhausted and was unable to think clearly. Definitely do get rest next time. Take NyQuil.
I'm sure you would have gotten higher than 157 too, because even if you're not feeling entirely drowsy, you're mind is working much more slowly than it would have had you gotten a sufficient amount of sleep. I encounter this problem whenever I have a sunday TM class because I usually go to bed late, skip breakfast, and don't have lunch during the break. I'm going to make sure not to make all of these errors in judgment before my second diag too, which I'm actually very excited to take. Can't wait to see how I do.