You could adjust your medication times to accomodate your work schedule so that you're not feeling sedated at work. I work the evening shift at my work (I'm in a health profession, also and have bipolar) it's only 2-11pm but I changed what times I take my meds and it's worked out fine. I take my wellbutrin which is fairly stimulating at around noon so it lasts throughout my shift, and I take my Geodon around 9pm so that I'm tired when I get home and can sleep. I don't know if you have an option like this, but it's just an idea.

Also, I only work 4 days a week, and I find that having 3 days off allows me to really recuperate. Having 4 days off yourself could be enough of recuperation to make it okay to work the 3 12s.