Hi Marzeater
I really wouldn't advise going to bed on a 3.4. That truly is a hypo. How did you feel? Did you have any symptoms (shaky, sweaty, hungry, generally feeling ******)? You had the right idea about eating something for the 3.4 but a whole bowl of Frosties wouldn't be the right thing (as you point out). Good hypo treatments are a few jellie babies, fruit pastilles or skittles (but not too many!) or, what works best and most quickly for me, is a small amount of Lucozade (I don't really like the taste so it's not tempting to drink too much of it).
So, to answer your question, I would say 3.4 is certainly too low to sleep on and shouldn't be attemted as you might not be able to feel how quickly you are dropping!