What do I do as a depressed TA?

My mental health is declining and as a result I haven't been a good TA. For example I let my students out of section early because I was too tired to present some of the material, and I did not understand some of my section notes because another TA prepared them, and I didn't read them in advance.

I also have trouble helping students during office hours, and often ask students to repeat themselves, and I don't do adequate preparation (by reading the solution sets in advance). I often don't know how to answer questions and I ask the students to collaborate with each other and solicit help from people who have already solved the problem. I wasn't the best TA to begin with, but now that I'm depressed, I am basically useless, and embarrassingly so.

I feel pretty bad about this and I am also terrified that my students will complain to the professor, who is friends with my advisor. What should I do? I haven't told the professor or anyone about my diagnosis (of bipolar disorder). And I am afraid to talk to the people at the school counseling center, because they might force me to take time off (this happened to me in college), and I can't really do that in grad school without irreparably burning bridges.