The update is that I haven' resigned - just about managed not to, have dragged myself into work on Monday and Tuesday but am now off sick - both cold and stressed out / overwhelmed.
I went to Occupational Health today and the nurse said that I have to be careful not to run myself into the ground. She advised me to contact HR and my GP.
I'm not sure whether I'll make it in tomorrow or on Friday...
I've never been off work for long for stress-related / depression- or anxiety-related reasons. When are things going to improve for longer?????