I have no motivation lately.
I stopped studying for a few days so I am forgetting the words that I thought. = the words that I've learned
I'm going to go for a business trip tomorrow so I'm not sure if I can attend my class. = on 
I knew that i had to start studying again but I'm feeling doing nothing. = know ; I'm not feeling it right now/I'm feeling like doing nothing.
I appreciate it. 

Hi Jane! It's okay if we won't meet tomorrow. I know you've been feeling less energetic lately, I could see it in your eyes. The best for you to do is to unwind, contemplate, and finally have courage to resolve anything that are bothering you. Take it easy!