I use to be a cardio maniac, so I'll give you then and now answers.
Then
1. 3 buddies and I made our own par-course over a 2 mile path. There were a dozen stations ranging from low roundhouses to certain trees, forearms, slipping drills, etc. The track came close to one point about 6 different times, so the non-runners could take part in the station, holding pads/mits, striking the runner and such for each drill. The last station was the other guys waiting in line. Each holding a different weapon or none at all. You'd have to take them out. If you failed, they chose which part of the course you had to run to, then come back and try again. Anyway, one day we decided to see who could do the course the most times consecutively. I eventually lost, but I tried so hard I was sure I was going to die. I don't remember hurting that bad in training. It sucked.
2. Just a really good sqaut day. I tossed my lunch after a few sets. Went back and sueezed out some more. I then started to pass out and lost most of my vision in my right eye, and it didn't come back for a couple hours. That kinda scared me.
Now
1. I walked to the refrigerator a little too fast the other day and had to sit down for a while. Phew
2. Same thing, squats