Hi Mr James Chapman,
Thanks for posting your query.
The symptoms your are suffering from may be related to thyroid disorders and diabetes
Thyroid disorders especially hyperthyroidism
may cause such problems.
Therefore you should go for following investigations -
1. free thyroxin (FT4) and thyroid stimulating hormone
2. fasting and post-prandial blood sugar (FBS and PPBS)
Primarily these two common disorders have to be excluded for your symptoms.
If any one of them has a positive result you should consult an endocrinologist