I'm a native English speaker but I went to Spanish camp here in the USA in high school for four weeks so here's what I found anecdotally about that experience helpful - in a nutshell what happened is I started having dreams that were in Spanish, which helped me a lot as far as being able to access words/phrases quickly in the context of speech because I was starting to think in Spanish too. Academically, when I went back to school it didn't really make me a better Spanish student, but in the real world having to listen/speak it's a game changer.

As far as to the why/how I started dreaming in Spanish, I think it was how the camp was structured, the camp counselors from Spanish speaking countries made you speak Spanish if they caught you speaking English, which we did since everyone there was a native English speaker, but I just remember counselors rolling up and saying "En Español!" all the time if they caught you, so we'd have to speak it. If there was one strict rule of Spanish camp it was "En Español! No Ingles!" (paraphrasing here perhaps)

If you're not dreaming/thinking in English yet, I'd recommend trying to get there as a measuring stick because then you can literally improve in your sleep. It certainly used to be a commonplace occurrence when you were "immersed" in something, but a knee-jerk hypothesis might be that it is harder to be immersed in today's always-on + connected world. You can probably binge watch any TV show from your homeland, talk to anyone in your native tongue without insane long distance charges or waiting for the mail to be delivered, etc.; it would be understandable, but those things probably have a counter-effect to the goal I'm describing, and those things require some discipline, at least to teenagers at Spanish camp from my experience.