Leonidas, I am not clear from your post what you did. As I understand it, an immersion course means to go to some Latin country and do all your communicating in Spanish, 24x7, unless you need to call home.
Is that what you did, followed by the interactions that you describe after you returned to the US?
Ha
No, it was actually two classes (beginning and intermediate) and it was in the US (Houston and Miami). It wasn't immersion in the sense that it was 24 hours a day, but it was 8 hours a day of being pushed to communicate only in Spanish. The beginners class had some limitations, especially in the first few days, but even it moved rapidly toward Spanish being the only means of communication. They gave us a ton of written material for vocabulary purposes, and it had the English translations, but within a couple of days the instruction was almost exclusively in Spanish. It was a lot of vocabulary with much leeway given for poor grammar.
It wasn't too tough for me because I had taken beginning Spanish in HS, college and at work. I experienced a lot of improvement, but the guys who came into the class knowing only Taco and Cerveza were darn close to me by the end of the class.
The intermediate class was 1000 times tougher. It was all Spanish all the time and rapid fire doesn't begin to describe how quickly it moved. They were picky on grammar, and we had to be able to use multiple tenses of verbs in a single conversation. Every morning started out with you describing what you had done last night or that morning before class, what you were doing at that moment, what you were going to do later that day, and what you might do in the future. For lunch we were sent to places in Miami where the staff didn't speak English. We also ate some dinners in similar places and we were only allowed to speak Spanish during the meal. They would pass out a newspaper, or show a video of the news, and then start a conversation about what we were reading or watching. Those conversations were tough because they would always go way beyond the text of the article and make you talk about your opinion, analysis or beliefs about the subject. Every night there was a section from a book or magazine in Spanish that you had to read and understand, because there would be a hour's discussion on it the next day. Or you had to listen to a Spanish radio station and come in the next day and sing a song you had heard - or
screech a song in my case.
By the end of the class I'm not sure I can say that I was thinking in Spanish, but my mental translation process was nearly instantaneous. By that I mean that I was no longer doing the cumbersome process of translating what I saw or heard into English, thinking my response in English, translating it into Spanish and then speaking it. I would comprehend all or most of what I heard or read and I would find myself responding almost as quickly as if I were speaking English. We all still stumbled on new words, or occasionally screwed up the grammar, but the mistakes were generally small and we were effectively communicating solely in Spanish.
The other stuff was just practice to keep my skills up and try to improve while I waited for the annual testing period for language proficiency. It's easy to do when 20-30% of the people you work with are Spanish speakers, most of the "clientele" were Columbians or Dominicans, and you live in a city with 3 Spanish language TV stations, a couple of dozen Spanish radio stations, and about a third of the population is Spanish speaking. Plus we were doing wiretaps on people that were all Spanish speakers and I would spend at least 8 hours each week working the wire room and practicing my Spanish with the interpreters (luckily they were mostly gorgeous women who were occasionally given to being flirtatious, so I was highly motivated).