are my fish paralyzed?

[iamatwilighter:t]

Could it be that my poor fish are paralyzed? Two of my fish try to move but they can't seem to move their tails and backs, they're sort of crawling at the bottom of the tank trying to move with they're fins. Some say that they could be depressed and that they'll just give up and die, one of my older more beautiful fish died about a week ago, might that be the reason of the possible depression? another thing i've heard is something about swim bladder. i don't know what that is. can someone please help me find out what's wrong?