Re: HR involvement
"Regarding involving HR, always remember what their job is: they exist to protect the company from the employees."
That's true on both side of the Atlantic.
A top UK university's HR department happily threw me under the bus(*) when I was suffering from burnout. It was only the intervention of senior departmental staff which allowed me to stay.
(*) After umming and ahhing for 3 weeks, then deciding it was too hard. An hour's consultation with a lawyer changed that tune rapidly but they still didn't want to keep me on, whilst the department did.