Yeah, that's how I was diagnosed as well. Thought the vomiting was just something I'd eaten - didn't even think about diabetes because I'd seen my GP about diabetes a few months before that, and he'd told me I was fine after a fingerstick test.
I, too, had to spend three days in ICU; on the positive side, I was seen by the DSNs and a dietician right away and learned 95% of what I had to know before leaving the hospital.
I don't know about blackouts, but if you're in any doubt you can probably call the diabetic team at the hospital. If you don't have their number, call the hospital switchboard - they'll be able to help you.