Holy crap. I know they say to be careful to adjust to the altitude (13k feet here in Huancayo if I recall right) before doing anything strenuous but I didn't realize how bad it was. This morning I felt fine and decided to see what's up, so I started my morning wakeup routine of pushups/situps/handstands.
Um, yeah, no. About 15 pushups in I started to feel a weird spike of pain in my head and I decided to keep going. At around ~25 pushups I almost blacked out. Seriously. My vision almost completely disappeared accompanied by migraine level waves of pain. Even 30 minutes and two excedrin later I'm still wracked by these spikes of pain in my head and a low level of background pain.
All this from ~25 pushups... I wasn't even breathing hard and my muscles weren't even noticing it yet. Insane. Methinks I will be taking it a bit easy for a couple more days.