Thanks for the replies.
I've had a course of counselling sessions last year that helped sort a few back ground issues, but the medical/chemical imbalance exists irrespective and has done for the last 25 years or so.
I went to the Doctors again this afternoon after a very rough weekend and she has agreed to refer me to a consultant psych specialist to see what's what.
This is a source of some hope - of what I'm not sure, but it's a step in the right direction.