I keep a daily log of my symptoms and bring it with me to appointments. I can look back and see if I overdid myself a couple days ago and compare to symptoms today. I made an excel chart and filled in which symptoms I had and can look over the month and look for trends.(I am a bit OCD!) I look at worsening breathing, fast heart rate, Exhaustion/, Post exertional Malaise, Headache, sensitivity to light & sound, Muscle Pain, Sleep Disturbance, Chills, Balance, Sweating, Memory/Recall, Brain Fog/Concentration, Word Finding, Spelling, Nausea, Appetite Loss, ringing in the ears, days I've had to cancel plans because I was too exhausted, working beyond my 2-3 hour limits for each cognitive and physical activity per day
My best personal test is Sudoku. Every morning I do a puzzle from the same degree of difficulty (from Sudoku Deluxe app). If I cant solve it, I know I am not tracking well that day-abstract thoughts, patterns, number recognition. I know I shouldn't be doing critical thinking tasks that day like financial/legal decisions.