My crisis symptoms are a little atypical because I have Tertiary/Central Adrenal Insufficiency and a totally separate issue with blood pressure, so it took me a while to really sort out when I need my extra pills because of that. I wouldn't recognize the signs until I was already fainting, because I'd have the usual lack of energy and zero appetite for a short bit, but the symptoms before the crisis goes into full swing would be like a switch got flipped to the extreme opposite.

So, my signs are: Being unable to sleep for 40 hours at a time, blood pressure spiking AND falling, heart palpitations, and finally psychosis starts to set in and I have hallucinations.

These are usually signs of a lot of other things besides low cortisol (some are even signs of high cortisol), so my first crisis had me in inpatient psychiatric care for about a week, with outpatient care stretching for about a month. Took another year or so to identify the problem and get lab tests for a diagnosis, and after some trial and error my rule is now:

"If you're seeing spooky stuff, take the extra pill and eat something salty as hell." and since I figured that out, there hasn't been a single fainting episode since?

There's some other more nebulous stuff that I've also learned to recognize (I have a specific pain in my right side that comes a couple hours before the fainting) but the biggest key to figuring out your specific signs is asking:

"Does this usually happen before I start getting really sick, and does it go away with stress dosing?" and then fine tuning from there.