Losing the plot

I am losing focus badly at work.  It has been noticeable over the past month or so, I am not as quick as I used to be and seem to have lost the knack of pre-empting what the dentist needs.  I find it hard to concentrate too, and I am finding this at home, my thoughts are going around in my head at a hundred miles an hour.   I had a chat with the dentist about it and he has noticed, well, hard not to to be honest.  He feels it would be better to just book check ups in and short treatments on the days I work.  Thats no good is it?  Why should he have to work like that just because his nurse is losing the plot?!  To watch me sometimes you would think I have just started in the job, not been doing it since 1979.  I don't know what is happening to me.  Maybe I need a break, short term or permanently.  I don't know what I could do though if I left.  Working the 8 hours is too much on occasions.  I can't stand up for any length of time, I drop things regularly, can't concentrate, and am continually tired.  Not much hope is there.    I was really upset when James chatted to me earlier, I guess I was trying to kid myself it isn't happening.  Oh bollocks!