Hi Rachel, geeze that's scary indeed!! I'm generally pretty aware of going low around 55 or so, but have on occasion had it just sneak up on me. My lowest "recorded" was 42, but that was AFTER I'd already begun treating the low! (I can go into "survival" mode and I don't even think about testing, all I can think is I need CARBS and need them NOW!! LOL)
In general, I think most people tread with about 15g carbs for a low, and then test again in 15 minutes. If you see that your numbers have risen, but still not to an acceptable level, maybe try 10g more, and again test in 15 min.
I have those little bottles of Sunny D (6.75 oz bottles, comes in a 6 pack) that I keep around, for when I go really low. They have about 26g of carbs (depending upon which flavor you get then +/- a gram or two). If I find I'm in the 40's I'll just drink one of those an it does the trick!

Only ONCE, did it not! Took me about an hour to get out of that low! I thought it was never going to end! YikeS! But finally it did. Though I think I ate everything in the entire house along the way! LOL