I was in this boat about 6-7 years ago during my undergrad years. I remember one year I took 22/23 units per semester (mostly upper level science courses-like biochem, physiology, genetics, molecular biology etc), while working 30 hours per week, and participating in a bunch of clubs. I thought I could juggle things. Well, maybe I could have... except that my grandfather died mid-semester, and two days after my grandfather's death I found out that my significant other left me for another woman. (This was shortly after the 9/11 attacks, which was already a stressful time to begin with.) Let's just say that at that point, everything I was juggling hit the floor with a crash... I fell into a dark depression, and started having panic attacks. There were times when I didn't leave my apartment for several days, and spent most of the time in bed. One night after organic chemisty class, I walked into the bathroom, and collapsed on the floor... I was not well, but I keep pushing myself regardless.
I still managed to do quite well that year overall, with a 3.0 during the first term and a 3.8 the next. However, I got my first C's in college, in ochem and genetics. But the depression was wiping the life out of me... I was very emotionally drained, and completely became isolated from everyone else. I was still nice and friendly as usual, but I was in a lot of pain.
Looking back at that dark time in my life, if I could do things differently I certainly would have lightened up on my course load. There was no reason to be taking so many courses. I really needed to cut myself some slack.
For med school as well, it would have certainly benefited me to have taken less classes and gotten A grades, rather than taking 22/23 units and getting C's. That year took a hard knock on my science GPA, from which I still haven't recovered. Now, seven years later, I am applying to med school... and my science GPA is still low. I still have a great chance of getting into DO programs (which is just fine, as I am very interested in osteopathic philosophy and holistic medicine), but it would be nice to have more options.
So for both your personal health (which is of foremost importance) as well as your future medical career, take some time to cut back on classes (if you can). If you can take a semester medical leave, or a semester of easy classes, I recommend that. Also, taking time off may not be good enough by itself. It may be wise to combine an easier schedule with other things to benefit you... such as by going to your schools mental health center (you can be screened for depression there). If you do indeed have depression, you may be referred to a psychologist (for talk/behavioral therapy) or a psychiatrist for meds. For me personally, I only took meds for a short time, but had to stop taking them due to side effects. So it forced me to have to deal with things differently... such as by eating a healthier diet (I got into raw foods, veganism, etc, which helped significantly), spending more time with exercise, taking supplements (like omega 3, amino acids, etc). You'll have to play around with things to see what works for you. Maybe making a conscious effort to spend more time with friends and family will help too... assuming these people are supportive, and not negative.
Please take care of yourself. None of this is worth anything if you don't feel good. Going through med school is supposed to be a hard enough experience in itself (and many people get depressed AFTER starting med school), so you want to be as healthy as you can before starting. Please make sure you feel really good again... just getting by in your classes while feeling somewhat lousy isn't good enough.
