4.1 is great for your first day of low carbing. As
@Kristin251 says, the shakes will have been a false hypo - but I know it feels a lot like the real thing and more than a bit scary.
I have come off of Lantus and Novorapid (which are slow and fast acting insulins) and other diabetes meds - I'm just on Metformin now - and it was a long slow process but very much worth it. Only come down one unit at a time and then wait a day or two before reducing another unit just to see how your body reacts.
Have you asked for help from your GP or DN? I know mine weren't particularly helpful but it worked out fine for me in the end and they are now convinced it was their advice that helped me get my BG in control. Bless 'em.