Awkward.
I hit some kind of crazy glitch-- I don't know what happened. I got to the heart stage, and when I clicked to accept the mission, my controls no longer worked. I couldn't even move my cursor up to the X on the window to close it! The pill spazzed and seemed to have taken control of my mouse.
I was then taken through what seemed like 4-5 missions but at warp speed, hitting enemies left and right and seeing the doctor screen flash up numerous before another level would pop up. This went on for about 20 seconds until I stopped fighting it.
I finally got a stable doctor's screen, and I was back at mission 2. I took care of the odd colored blood cells, but then at the "protect the heart" mission, I let it get hit by two blood cells, it turned gray, and then the game spazzed out again. This time, the mission restarted after a white flash and my cursor stuck right to the pill, so it would pretty much only spin in place no matter what I did with my mouse.
Again, I couldn't move my cursor to the X on the window to close it, so I had to Alt + F4. What the heck did I do?