We had exactly the same experience with absorption problems last weekend.  We knew Claire (age 8) had strep, and she was getting triple Cortef, antibiotics, and had no problem keeping down lots of fluids.  She was peppy and alert before bed Friday night, and seemed fine when I woke her at 2 hour intervals through the night (I really recommend doing this).  Saturday morning I found her on the floor at the other end of the house.  She had gotten up to get another drink and was too weak to get back to me.  Extreme muscle weakness is an indication of adrenal crisis.  She was back to normal 1/2 hour after the injection.   Getting the injection is traumatic for her, so we hate to do it if it isn't necessary.  The doc assured me we did everything right, but it makes me crazy that I can't tell if she's absorbing the oral Cortef!  I've always felt like I could sense when she was in trouble.  This one took me completely by surprise.  She complained of back pain that morning - I was afraid from falling due to weakness - but it cleared up after the injection.