also need to consider if you had any unusual exercise anytime prior to the episode as long as 1 day before it. Or were you sick before it. Any kind of infection will mess with BG levels as well.
Two thoughts I have come to mind. First is it possible that you had accidently switched you long and short acting dose, that can cause an accute low like that.
Second you said the hospital measured your insulin to see if there was too much but came back normal. Was that after the glucse drip and you BG came back up. I would think that if is were after you were no longer low, then the current inslul level would not be high since whatever insulin was there had been used by the blood sugar you drank and recieved via iv drip. That info would have only been useful if it was based on blood drawn when you first got there not when you were finally stabilized.
I wonder how long you have been a type 1 diabetic -- could you still be honeymooning, occasionally producing some insulin of your own? What preceded this event -- did you participate in anything stressful (good or bad stress can cause me to drop low)? Also, how old was your insulin -- if you use a long-lasting insulin like Lantus, if it is older than 1 month old, it can misbehave. I notice that I get "dumps" of insulin and will drop low during its peak time at about 4 hours after injection, or at about 5-6 pm, when I think its crystals just give up the ghost and cease to release slowly when my insulin is old.
Your situation WAS extreme. The questions above may help you figure out what happened, or maybe the drop was due to something else that affected the endocrine system. So much is inter-related. Did you take some allergy meds earlier (my sister will have severe drops after taking allergy meds or coming inside during allergy season)? So much can mess up our routines. If you can figure out some possibilities, maybe you can protect yourself, but if not, then you may need to keep lotsa juice handy for awhile to see what happens.
If it happens again, it may be time to stay at the hospital and have your endocrinologist notified so more tests can be run. Good luck!