What is this?

I don't know why, but I'm having an extremely hard time thinking. Well, constructive thinking. I know that I'm still able to blink, swallow and move so my basics are down pat. I used to be so smart. Now, what seems all of a sudden, I am having a hard time thinking through problems at work associated with numbers (and numbers is my thing, so this is upsetting). 

I am also not quick witted like I used to be. I'm known for my sarcastic sense of humor and ability to take one thought and quickly turn it into another. 

I'm just upset about all of this. I've made too many mistakes. I'm dull. And it's causing me to blame everyone else. It must be their fault.