MS1, FWIW:
My lesson to you: do not discount your previous clinical education.
Medical school is hard, but it's not impossible. From what I can tell, medical education has found an absolutely brilliant way to select for very smart and intelligent people, pile them in a room, and relatively ensure that 95% of them have the brains and drive to become doctors. So, in this regard, it's not like climbing Everest without oxygen or any other event in human experience that requires extreme ability. But it is more like this:
Every day someone will take you out front of your home, at say 8 AM (that's when lecture starts), and flog you with books full of knowledge. You're expected to absorb 70-85% of the knowledge associated with each beating, with progressively more absorption per strike. The floggings will start out slow, but a beating is, well, a beating. It's not pleasant. But the beatings will grow in intensity and they don't stop...for 7-8 years. There is a culture in medicine, perpetuated by physicians, that medical education is "grueling." Our professors use that adjective more than any other to describe their days learning to become physicians and they enjoy, with strange admiration, passing that experience on to their students. At first it may come off as a weird form of hate and discontent, but it's actually affection for the process. They believe that good physicians must endure this same curriculum, complete with this underlying understanding that it must be hard. The reality is that there is a tremendous amount of information to absorb and assimilate in order to take care of people. This is especially true for our generation, where never before has their been a better understanding of the biochemical and genetic causes for a variety of diseases.
Getting to medical school is hard, but it's hard because it allows faculty to select for individuals who are most likely to succeed, i.e. tolerate the beatings. They need to put a ton of information down your throat (fire hose analogy) without you throwing up, i.e. dropping out. Faculty can make it hard without a high likelihood of them loosing their entire class. Few other professions do such a good job of selecting for such a cohort, and I'm sure we could argue about the downsides of this method of selection. One of the really cool things about medical school is that, for the first time in your life, you'll be surrounded by equally adept learners. Maybe not geniuses, but the comparative olympic athletes of school. Everyone around you has taken the same courses, has the same basic understanding of the scientific process, and an appreciation for the value of education. Sure, some can cite Shakespeare and one or two will be able to tell you the finer points of how to build a bridge, but everyone will have a basic scientific foundation for learning the human body. Everyone is there to be a physician, a surgeon, or a researcher and everyone is equally motivated. This is still true for DO schools. You'll still be one of the 5% admitted for your particular seat, so don't believe the haters. I haven't met anyone who isn't bright and, because of the mission of the osteopathic community, I often find a good deal of non-traditional students like myself, which I think adds a great extra element to a class. For this reason, I believe DO schools are owed a lot more credit than is thrown their way. Many of these schools have expanded the window of MCAT and GPAs for accepted students and still routinely produce equally qualified physicians without high attrition. Bravo.
So, you're an RN. You'll still take the beatings everyday, but now you get to wear a heavy sweater on your back, so the beatings hurt a bit less. You took some of your beatings already, in nursing school. That's how previous clinical experience helps. It doesn't supplement the education, nor does it make you invincible or immune from the suck, but it does make it a bit easier to integrate the material, especially when one of the hardest things for many of my classmates is applying the factoid nature of medical school to clinical applications. You'll be able to do that easier. Good luck.