LOL. Sorry. I am not an RN-turned-med-student, but want to make sure you have at least some idea of what you're getting into.
For the first 1.5-2 years you will have about 4-6 hours of lecture to digest Monday-Friday. This will be accompanied by another 4-6 hours of self study each day if you want to be a good student. The content is orders of magnitude more difficult to comprehend than nursing school curriculum. If you do not have a hard science background (nursing is not), what may take some students an hour to get through may take you a day. Most schools have a systems based curriculum now, and there will be mandatory labs scattered in throughout the week. There will also typically be at least some sort of graded exam every 2 weeks. The big exams in each system are typically brutally long (3-4 hours), typically one every month. The other facet is that most schools are pass-fail. Yes, you can slack off and do the bare minimum to pass. This still requires a significant amount of effort. Bottom line: 8-10 hours a day of rigorous mental exercise M-F. Every other weekend spent dealing with exam prep.
The USMLE step 1, arguably the most important thing you do in medical school, will require you to lock yourself in the library for 10 hours a day, every day, for 8 straight weeks rote memorizing study guides and doing thousands of practice questions. I am not exaggerating.
The third year is similar to what you describe for nursing, just much more intense. On the worst block, surgery, you will have 2 straight months of arriving at 4AM, a mix of floor work and OR shadowing until 6PM, going home and studying until 10 PM, and repeating this 6 out of 7 days a week. The easiest block, psychiatry, will allow you to show up at 8 and leave around 2-3 most days. The other blocks are somewhere in between. Blocks typically run back-to-back for 12 straight months without a break (i.e., no vacation). Exams occur at the end of your block, and they are mostly responsible for your grade in the clerkship, which is a big deal for residency selection (bigger than your pre-clinical grades). We did not get any dedicated study time for these exams.
The fourth year is mostly elective. If you are applying to a very competitive specialty, your hours and work effort won't be much less than third year, and you'll be traveling all over the country. If you're applying for a non-competitive specialty, you can average 20 hour weeks no problem.
This is followed by intern year, which is orders of magnitude worse than anything I have just described. It will be the worst year of your life, but you'll come out of it barely, just marginally competent to perform basic care.
But Nah, lets just give 2 year nursing grads "graduate degrees" from an online program and let them function as primary care docs. Same thing, right?
If an adcom lets you past the gates, then you have the cerebral horsepower to do it (most of the population doesn't), so if you've made it that far, don't be scared. If you put the hours in, you WILL pass. You need to be emotionally prepared for what's ahead, however. I.e., the stress you refer to will be severely worse and you need to stay on top of it and make sure you are dealing with it before things snowball out of your control, which can happen in a matter of weeks.