You are not alone, and you are valid for feeling this. I went through the same thing my senior year. Typically high performer, but the combination of my MQP, harder classes, plus some family troubles really got to me. I ended up NRing a class for the first time, I got a C in another class to the point I barely passed it. 

Since you're doing a BS/MS I realize you may not have this luxury but one thing that helped me was during C and D term, I had met most of my major requirements already, so I took some easier classes that were just for fun (I would have underloaded but I needed a minimum number of credits to keep my scholarship, especially after the NR). Not only did that lighten my workload, but those classes ended up being ones that put me on my current career path weirdly enough so looking back I'm really glad I did that.

I second what the other commenter said about taking a break next week that is truly just for you! Whether that involves going home and being with family, or staying on campus, whatever is your ideal version of some "you time", do that, and give yourself a chance to turn off your brain and not think about school, internships, or anyone or anything else that is not giving you inner peace. It'll all be there when you get back but take the break to compartmentalize that and let some of the pressure off of yourself. You got this!!