Navy BMT? Scared a little bit! Gas chamber, communal showers, nco's yelling?

How is it like in the gas chamber? Can you pass out? Does it make you difficult to breathe? What about communal showers? Can you get up 15-20 minutes before everyone else gets up? I heard whatever you do in BMT, YOU'RE ALWAYS WRONG! and the nco's will always have a reason to yell at you. Is this true? What else should I know about BMT?