Disclaimer: I am not a particle physicist, but I have taken several physics and engineering courses at the university level, so I’ve spent a little time in that world.
What year of high school are you in? If these are choices you are considering, I am guessing you’ve already taken some physics and calculus. Believe me when I tell you that college-level math and physics are at the very least as intense as what you do in high school. Pressure increases dramatically.
However, as you learn more, particularly if this is a subject that you love, you will find that the nature of the work also changes. So, what you are learning now becomes a base of knowledge that you draw from later, and the types of questions that you will answer (and ask) with your work change a lot. In some ways, it is difficult for you to judge now what kinds of challenges you will face, because you will develop new skills to handle them as you move forward. Also, the further you go, the more support is available from people around you (if you want that).
If, as you say, this is something you really want – then you should not be afraid to pursue it. You will find that your classmates also struggle with the workload; everyone does. It is your own desire to learn about physics that will keep you going. What would concern me more are questions about making a living in your chosen field once your studies are complete. Is this something you just want to take classes about? Because eventually, the question will be whether you want to conduct your own research. Is that the kind of thing you can see yourself doing? If not, think about channeling your interests towards something like mechanical engineering, which uses many of the same mental tools, but has a much wider variety of applications (including academic research), so your employment options would not be as limited. Just a bit of food for thought.