i dont know if you read my 'welcome to thailand Cord' thread in the kickboxing forum, but it may help a little in adjusting to a different atmosphere of class/school.
My school is very much geared towards the teaching of and learning martial arts. We do spar, and we can go hard depending on individual agreement with the partner in question.
The thai boxing class I visited was for fighters and fighting. This can make a big difference to the atmosphere and content of you 90 minutes.
If you are going to visit gyms/schools geared towards fighting, you can only expect to meet aggression in the sparring environment- you are fighting a fighter.
Thats great if its what you want to do- that makes you a fighter too, and you can let loose with your own aggression in a consenting environment. There will still be rules, and the ability to tap/quit if it gets too much.
its not a geographical thing- the Dog Brothers are crazy hardcore in the good ol' USA. it just depends on the goals and philosophy of the trainers, and from there the students they attract.
You will be introduced to all these places by members of your family, and they have all trained in them and lived to tell the tale, so I suspect you will do just fine