This is a really simple one, but can you try a breathing exercise? Just slow, deep breaths, in through your nose, out through your mouth, for 3 or 4 minutes. That's to calm you down/ relax.

I don't know what people think of this idea, but have you tried self help books? They often have excellent techniques for things like negative thinking. I mean, if you can sit and work and every time a negative thought comes into your head, TRY to switch it off, don't engage with it, don't let yourself keep thinking about it. You'll be surprised how much each thought is actually your choice, once you NOTICE your thought you can stop it. Like, if your inner voice starts chatting away "I hate being sat here, and everyone is so annoying today...." if you are aware of your thought, you can tell yourself "stop", don't carry on with the inner chatter. (I'm not good at explaining this technique but I'm learning it from a book called 'the power of now').

I do sympathise moonturtle, I said in another thread how I hated a job I was in for years. I think if you're truely miserable doing that job then it's great if you can think of something you would enjoy more. Do you have any ideas?