Warning: It's gruesome

The Russian Sleep Experiment – Russian researchers in the late 1940s kept five people awake for fifteen days using an experimental gas based stimulant. They were kept in a sealed environment to carefully monitor their oxygen intake so the gas didn’t kill them, since it was toxic in high concentrations. This was before closed circuit cameras so they had only microphones and 5 inch thick glass porthole sized windows into the chamber to monitor them.