HI everyone, thank you so much for all your answers and kind words. I spoke with my rheumy nurse yesterday and he thought it was likely that the mood swing were caused by sulfasalazine so we decided to stop.
I can't tell you how relieved I feel. It was very disturbing to not recognise myself in my behaviour any longer. I felt I was turning into someone I didn't like and had no control over.
I am sulfa free for 2 days now so too soon to see changes but a huge mental burden has lifted.
The nurse offered Methotrexate and presented it as the gold standard treatment. I asked for a little time to reflect. I would really like to be drug free for a while just to find myself again. I think I also secretly hope that I won't have any of the RA symptoms anymore which is likely to be at best wishful thinking and at worse being deluded!!!
Anyway, thank you all for the support and for sharing your experiences with me. You have really made a huge difference to my well being and gave me the confidence to ask questions.