In every segment, there's a shift that happens when Week 3 starts. I've probably written about it before, because it's always a weird week. After two weeks of messing with your brain, your normal patterns (both physical and emotional) are scrambled enough that symptoms of Week 3 show up.
1. Energy drop. We started class on Monday a full 10 minutes late, when we're usually good at starting right at 9. Everyone was quiet and very low energy all day.
2. Incompetency. By the end of Week 2 you feel fairly competent in what you've been working on for two weeks. When Week 3 comes around, it all disappears and no one feels like they have any idea what they're doing anymore. Everybody gets extremely picky about who they chose to pair with for FI practice.
3. Irrational irritability. This morning, for example, we did an ATM that was difficult for me. All the difficult pieces of it made me generally frustrated, and because of the build-up, hearing Richard ask during the lesson if lying down was getting "better" pissed me off, because no, it was not getting better, and why should it be? (He had framed that phrase at the beginning of the lesson. There was no valid reason for me to interpret it that way, but it happened regardless. Classic Week 3.)
4. Breakdowns/Meltdowns. If it's gonna happen during a segment, for most people it will be during Week 3, maybe Week 4. My little episode this morning didn't turn into a full blown breakdown, luckily, but I did excuse myself from the FI practice that followed the ATM. The morning would have gone much worse if I had been part of that practice.
There are probably more symptoms, but those are the major ones I can think of right now. Luckily the week will likely get easier after tomorrow. The slump is usually just the first two or three days of the week, and then the energy picks up a bit again. Just have to be patient with yourself and others and wait it out.