If you have charisma, then you can send a message. Teaching is not an exact science, but it is a message. I know algebra and I memorized the order of topics to teach graphing linear equations. As you go up levels, students can handle more quantity of steps per day, but the system stays the same. I have the routine in my brain, both from teaching it over two dozen times and reading/talking about it in graduate classes. When you have nothing, as I did 4 years ago, you can't help but sense that it was all done for a reason. Steve Martin once said "It is possible to will confidence". It is necessary to will charisma. Be happy and smile. When you sense a class is missing the point and they may be thinking your not knowledgeable, be confident.
Be confident your lesson is yours and good days are a great feeling andwill return. Remember those days are a flash in the pan. I remember how hard it was to be good for a class period and how I had to will charisma. Whether it is teaching a group of unmotivated seniors a week before exams, taking over a vacating teachers classes 2 months into the school year, or asking to take the toughest students for your class be charismatic. A wise man once said feelings work outside in. Studies prove that to be true. If you are with a charismatic person and they are happy, you will be happy. If you are with a charismatic person and they are down, you are more likely to be down. In my career I try to get find feelings that are locked inside and make those feelings along with good ideas come out. That is why I smile so much.