For me it was the constant feeling that tasks and responsibilities and difficult decisions are piling up faster than I could process them.
Not just "I have too much work to do", but "I have too much work to do and every day it gets worse, and in the morning meeting my team will tell me they all have too much work to do too, and lots of the problems are due to bad tech decisions I took in a hurry a while ago due to inexperience and lack of time, and... and...".
Fortunately I had an understanding manager who spotted me shaking in the lift into the office one afternoon and helped sort things out.
Not just "I have too much work to do", but "I have too much work to do and every day it gets worse, and in the morning meeting my team will tell me they all have too much work to do too, and lots of the problems are due to bad tech decisions I took in a hurry a while ago due to inexperience and lack of time, and... and...".
Fortunately I had an understanding manager who spotted me shaking in the lift into the office one afternoon and helped sort things out.