I totally agree with KSshrewman, never run it while sleeping (and make sure you have proper ventilation when you are running it).
I narrowly escaped carbon monoxide poisoning TWICE during one of my hunting trips while running the catalytic heater all night with no ventilation, but I didn't know what it was until later. Both times I woke with severe dizziness and headache which lasted all morning. When I got home from hunting I went to the doctor for a checkup, including treadmill, and everything was 'golden'. My tent was a nylon dome tent with nylon floor and nylon fly over it, and all windows and door zipped tight against the cold......absolutely no ventilation!
I was very lucky to have survived it. - John