CRJ700 CAPT REPORTS BUMPING HIS HEAD AND INADVERTENTLY TURNING OFF BLEED VALVES; CAUSING CABIN DEPRESSURIZATION.

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AT FL380; I INSTRUCTED THE FO TO PUT ON HIS OXYGEN MASK BEFORE I STOOD UP TO GO TO THE LAVATORY. I STOOD UP AFTER HE HAD HIS OXYGEN MASK ON AND BUMPED MY HEAD; BUT DIDN'T THINK ANYTHING ABOUT IT BECAUSE IT WAS NOT THE PROVERBIAL BATTERY MASTER SWITCH. AFTER LOOKING THROUGH THE PEEP-HOLE; I TURNED AND IMMEDIATELY SAW THE CABIN PRESSURE RISING AND SAT BACK DOWN; PUT ON MY OXYGEN MASK; ESTABLISHED COMS WITH MY FO; AND IMMEDIATELY ADVISED ATC THAT WE NEEDED TO DSND. WE WERE GRANTED FL340; THEN FL240; THEN 10000 FT. AT FL240; THE CABIN ALT CAUTION MESSAGE ILLUMINATED. THROUGH FL200; THE CABIN ALT WARNING MESSAGE ILLUMINATED. WE SAW PRESSURE RISING QUICKLY AND APCHING THE 14500 FT MARK. PAX OXYGEN LIGHT ILLUMINATED. I MADE A PA TO THE PAX (FLT ATTENDANT COMMENTED THAT WAS ILLEGIBLE). AT 10000 FT; WITH ALL EMER DEPRESSURIZATION CHKLISTS DONE; WE HAD TIME TO SEE THAT THE BLEEDS WERE CLOSED VIA THE EFIS. I ASKED THE FO IF HE CLOSED THE BLEEDS DURING THE CHKLIST. FO SAID 'NO; IT'S NOT PART OF THE CHKLIST.' I REOPENED BLEEDS TO 'AUTO' (NORMAL SETTING) TO PRESSURIZE WHILE AT 10000 FT. I REALIZED THAT I PROBABLY CLOSED THE BLEEDS WHEN I HIT MY HEAD -- APPARENTLY ON THE BLEED VALVE KNOB. I MADE A PA AGAIN UPDATING THE PAX AND FLT ATTENDANTS THAT ALL WAS NORMAL AS NORMAL COULD BE WITH PAX OXYGEN MASKS DEPLOYED. WE CONTACTED DISPATCH WITH THE SITUATION AND AGREED WITH DISPATCH TO CONTINUE TO DEST AT 10000 FT. LNDG WAS NORMAL. ADVISED MAINT AND OPS AFTER LNDG.