I'm at SB. "Pre-med," courses have a pretty rough reputation at Stony Brook; General Chem I (CHE 131) has the highest rate of students dropping out throughout the semester, supposedly. Cell & Organ Physiology (BIO 203) has the highest failure rate, although I don't see how one would easily confirm this.
Stony Brook is a really tough school, and a lot of people (myself included) entered as freshman thinking that they would breeze through because they have a 4.0 in high school. It definitely takes effort to get A's here. With that said, it's certainly feasible. Professors don't want you to drop out of the class or fail. Since it is such a large school, you have a lot of freedom with arranging your schedule (which is a very good thing). Also, there's a lot of resources for you if you are having trouble (Chemistry Learning Center, Math learning Center, Bio Learning Center).
So that's the positive stuff; there is some negative stuff, too. Chemistry and Bio classes have roughly 500 kids per lecture. There are rarely questions asked during lecture, so it truly is a lecture: a professor speaking with basically no interaction from the students. If you fall behind, the course will not slow itself down. Tests are very difficult (class average on Chem tests is around 60 at highest, I'd say), but doable with a lot of studying. I think Bio is a lot more forgiving.
Oh yeah, take the non-engineering Physics; it's called Physics for Life Sciences 1 & 2. I took engineering track physics, and it was real challenging (I remember a C average on tests was as low as 20/100 at one point! it was THAT ridiculous).
To wrap it up, just remember that your success is a function of your effort. Don't fall behind, stay positive, and have fun. You'll do fine. I hope I didn't scare you or anything, just trying to give you an insider's look.