What is your cardinal symptom that you need to rest?

Do you have a warning sign that you’re pushing too hard and need to immediately stop?

I don’t mean PEM, I mean the quiet or not so quiet warning that you’re causing PEM.

I’m still trying to identify mine. I can get a bit headachey (but with high frequency episodic migraine it’s not foolproof) when I’m pushing too hard and I think I start getting clumsy before any other symptoms show up.