If you ever been to a doctor/dentist and needed to be knocked out those gases are weird... I had this done to me once when I was I think 4 to have 4 teeth removed iirc, they made me wear a mask that had Popeye on it and some funny smelling gas was pumped into me, when I came to they were stuffing tissue in my mouth to wipe out the blood....
Bajie said it's poor man's opium so must be some funky gas they're inhaling. Anyone that's held their breath as long as they could would know it is an odd sensation! As for inhaling stuff... Many people find the smell of petrol intoxicating, I know I used to as a kid... Messed up era they live in but I don't think it's any drugs, short answer they are messing with probably some industrial gas they can get cheaply (Hence Bajie calling it poor man's opium) (They could be inhaling exhaust fumes etc anycase it's definitely bad for their health whatever they're doing!)