I guess the advantage of retaking would be that (1) you get a better understanding and (2) DO schools replace the grade. So with that in mind and you really want to see and learn the material, go for it.
Like I said, I had a C+ in physics I calc based. I had this guy from cal-tech teaching the course who was ridiculously hard and so awesome. He didn't believe in curving. So like 4 engineering students got As. No kidding. I was so freaking proud of my C+ I feel like I have a better understanding of some things in that course than others that I got an A in. He took a week to talk about 4th dimensional space-time FOR FUN. The quiz was like, describe how you would draw a cube in the 4th dimension... haha. So I fully support you taking it for a better understanding. Sometimes the grade does not reflect understanding, which is why I didn't retake this class. And, if you understood the EK physics, don't worry,
About the health issues...I had chronic migraines until I got on the right regimen and switched docs I had a few Incomplete grades. Adcoms asked about it, I explain it and it wasn't a problem at all. Just be really proactive about your health.
I also think maybe taking a lighter load at your new school would be good so you can adjust...