Tough days... we all have them as teachers... we deal in a human occupation and so there is no way around them! Our days are impacted by how our lessons go, how our students react, administrative treatment, etc. On the worst days it can sometimes be hard to remember why you should keep going and come back to work the next day. (I know I have had those days!)
In order to cope with those bad days, I usually start by sitting down and having a good cry. Yep, I'm one of those people. Then, I go across the hall to my friend C and vent about what went wrong (and how to fix it in the future) and let her tell me how wonderful I am (the compliments always help!). I also keep positive notes from parents, students, etc. handy to read when I'm feeling like I am a horrible teacher. Those help to put things in perspective for me.
Once I get home, I don't do any schoolwork that night. I make myself some dinner, spend time with some trashy TV shows and with my husband. Helps me unwind and forget about the day and get up the next morning refreshed.
In spite of the occasional bad day, I feel so blessed to be able to work in a job where every day is different and where I enjoy going to work.