AHHHHH (rant/advice?)

THE COUNSELING CENTER CALLED BACK TO SCHEDULE AN APPOINTMENT IM ACTUALLY GETTING THERAPY HOLY BALLS!

What do I do? Am I talking first? Are they talking first and prompting what I talk about or do I just pick a problem and run with it until im out of things to talk about in that topic and pick a different topic? Do I mention the most important things, or the relevant things, and what about the less important currently irrelevant things? Cause I cannot for the life of me mention all of it in one sitting without crying myself into a panic attack or even worse, a migraine(don’t come at me but 24 hours of hurling and pain is worse than my fight or flight going into death mode for a singular hour imo).