I haven't been diagnosed with anything, but I can relate to a lot of what you're describing. Sometimes I'm on top of the world- I start crying at the grocery store because the fruits and vegetables look so beautiful. I also feel elated sometimes when I see the sun shining or a breeze hits me just the right way. I get things done that I've been putting off for months or even years! On the other hand, sometimes I struggle with meeting minimum expectations and don't leave my house for a week. I sleep for 16 hours (or more) a day and avoid interacting with anyone. I've screamed and cried so loud before that my neighbors thought I was being attacked and called the police. The police wanted to come inside and look around when I explained that I was alone and that nothing was wrong. It's hard for me to maintain close friendships, even relationships with family, because I can only stand so much socializing- even with the people I like the most.
I always manage to do what I need to do to, though. The pets get fed, etc. And although the negative thoughts can be overwhelming, I've lived like this long enough to know that they're temporary. My mind knows that I have every reason to be happy, even when my emotions tell me that I'm suffering.
As for nursing, I do fine at work and can put on a good show- even when I feel terrible. I've learned to moderate expression of my moods, although the feelings inside have not changed. I'm also good at not reacting to other peoples' bad moods. I understand and accept them, at least for the most part. Keeping stimulation to a bare minimum when I'm not working helps me a lot. I'm also married to someone who appreciates alone time and is not emotionally needy. The relationship provides a lot of support for me without being too demanding.