and my poor uncle tucked in the grab loop (I gave direct instruction as to avoid this).  He remembered and looked down to see it tucked into the cockpit.  He then proceeded to pop the skirt and reapply in the foot deep water.  About this time he looked up and saw a pretty beefy wave about 10 feet out and curling perfectly.  So he hastened the attempt and much to his disliking, he noticed he had tucked it in again.  He had no roll and got destroyed by the wave which washed him back into 10" deep water.  
This is where it gets funny.  He fell victim to panic and couldnt get a hold of the skirt in the water.  So his head was pretty much on the sand and the kayak was resting on it's side.  BUT when a wave came in, he would try to get air by pushing off the bottom, but the water was now around 2-3 feet.  He could barely gasp at air.  I was about 40 yards out and thought he was playing.  The wave would let out and I would watch the kayak come to rest on it's side in shallow water again while he was working on the skirt.  This terribly mistimed sequence happened about 4 times!
THEN I saw the flailing jerky movements that indicate someone is REALLY trying to get out. His arm went up into the air and I yelled at my dad to help, but he was watching some storm clouds in the other direction.  I paddled like a mad man and thought I was about to kill my uncle in 10" of water.  
He managed to just grab a handfull of skirt with both hands and jerked it off.  I came surfing in to see him in shin deep water "sure" that he was in 4' of water the whole time.  He learned to roll the next day and we had a bunch of laughs after the "I almost died" feelings wore off.  
But as for shallow water, sometimes try to grab the rock and right yourself with it.  If it is shallow enough to pin you to your back deck (barring a forceful pinning situation), you can probably push off the bottom.  I know its easier said than done - esp. for a relatively new paddler.  But you can always learn from a bad situation.  Being back deck not on purpose is never good though, and without a paddle - worse.  No shame in swimming, if you had come upright, you might or might not have been able to stay that way without a paddle anyway!  It will make a great story later!