We Cushies have to go to the emergency room when we face adrenal insufficiency and adrenal crisis. I'll post some additional links (here), (here), and (here).
Tip #1: Stay focused on what you need
Dehydration, infections, and the inability to keep down oral cortisol replacement cause Cushies to take the dreaded drive to an emergency room. So before you get there, psyche yourself up on the ride over. You better mean business, or you won't get the help you need if you don't push for it.
When checking into the ER, I present my instructions from Adrenal Insufficiency United that states I should not be triaged. When the nurse tells me to sit down and she will be right with me, I refuse to go sit down. I ask that those instructions be reviewed by the charge nurse or ER medical director, and that I will there at the desk until nurse returns. This usually gets me taken back as the next person.