Do I need a stress leave?

I am so upset right now. I was supposed to be at work at 7:45am, but thought that I was to be at work for 8:20am. I even called at 7:45am (because I couldn't find my keys!) and told them I would be a bit late for the 8:20 shift. The girl I spoke with at work was busy when she took the call, and she said, "okay, that's fine", instead of looking at the shift board and telling me that I was actually scheduled for the earlier shift.
When I got to work, I was abruptly told by one of the senior techs about my error. She looked down her nose at me and said "you know that you were supposed to be here at 7:45 don't you? It was on the schedule. Fill out the time-in book as soon as possible."
The thing is, my boss just told me on Thursday of last week that my shift had been changed. I totally forgot. I have a daytimer and everything. I just completely forgot.

Somedays I think I should take a mental-health sick leave, but I know that would create more stress, as we wouldn't have much money coming in.
But honestly, I am so sick and tired of forgetting, not being able to emotionally seperate home and work, not being consistent in my quality of work, etc. I'm sure it's quite frustrating for my boss as well.
"Wow, Shelly's really improved in her performance...oh, wait a second, she just screwed up again..." is what I imagine her to be thinking, as it seems to be a cycle with me. Maybe because I'm a rapid cycler, I'm good at work when I'm manic, and bad when I'm depressed...? Could be.
I haven't been sleeping well either, which doesn't help anything. (I've been having a really hard time falling asleep, and once it's time to get up, I can barely drag my butt out of bed and into the bathroom on time to get ready).
Tonight we have my step-son coming back to us after 3 long weeks away at his mom's. I'm a little stressed about that, as he's always a handfull when he comes back from his mom's. Plus, when I'm not feeling all that well (bipolar-wise), my step-son and I don't mix very well. This is how it usually goes: I get irritable about the littlest of things - he calls me a nag - I blow up - he blows up - I start to bawl - he feels bad and says sorry - I say sorry while still bawling. There you go. That's the usual run of things.

That was yesterday.

Today I feel much more well rested as I satyed at the new place. I had some time to myself. I took it upon myself to increase my dosage of Lamotrigine by 50mg as I know that if I went to the doctors office, she would have done that for me anyways. (I know, I know...I shouldn't have, but I'm seeing her on Thursday and telling her about it!) I did some laundry, put some boxes away, set my coffee maker on program and then I crawled into bed. I watched 'Heroes' on TV at 10pm, and then I fell asleep and slept like a baby. It was so nice to wake up to fresh brewed coffee and a shower (if I haven't mentioned it before, our old place only has a bath!). It felt like I was at a hotel, all by myself. On the drive in to work I listened to some Joyce Meyer sermons. They were really uplifting. So thank you very much for your prayers. For today, this day, I am content.

Shebee