He hasn't got any amalgam fillings in his teeth by any chance?

Some of those symptoms sound like mercury poisoning - irritability and coordination in particular.

A blood test typically won't show abnormal mercury levels in the blood as the mercury tends to be bound in the cells. To detect it effectively you need to take a mercury challenge test where a chelating agent is used to pull the mercury out of the cells so it can be detected in the blood or urine. It's not something that should be done at home as it can be dangerous if it's done wrong and can harm the kidneys or liver.

I'm not a doctor so don't take this as medical advice, so I could be way off the mark.

I hope you can help him get over this and get back to normal.