My opinion is that this was just a dream - although a quite vivid one. Most likely you have been unsettled by thoughts of your diabetes going out of control, and this is your subconscious reviewing a possible scenereo. Of course, dreams can be combinations of more than one idea going on at the same time (such as the out-of-body experience).
I wouldn't see this as an omen, nor particulary a warning. Just a reflection of what's nagging you about your diabetes. However, it can be used as a good reminder of how important it is to keep the diabetes under control.
I just remembered that many years ago when in my 20s I had several sort-of dreams where I was "out-of-body" - not in the ER, but in my bedroom. I was rather fascinated by it and if I remember correcly, wasn't fully asleep, just at that point where one is beginning to fall asleep.