I'm thinking of not going to work
Oh really? Is there a reason that you don't want to go to work?
I don't want to do the difficult work
Wanting to take time off work is understandable but you shouldn't do it often. Unless you are actually sick or have an important appointment you are just taking off for no real reason and that looks bad in your employer's eyes.
Not really, I'm planning on just pretending like I feel sick and I can't do work.
It's true that most companies will let you take time off if you are sick, but you shouldn't abuse this privilege. You will still have to catch up on your work later, and it could get more difficult if you blow it off now. I suggest just going to work and doing the easy parts today, since you are tired.