6g per 100g seems very low. I just did a quick google and found 14g per 100g for carbs in a banana with skin (
http://www.myfitnesspal.com/food/calories/350164295)
As you do not eat the skin (unless you know about some special goodness that I do not), I would be more tempted to use the carbs for 100g banana without skin (
http://www.myfitnesspal.com/food/calories/generic-banana-raw-without-skin-100g-442254861?v2=false) and reduce the weight of the banana by the typical weight of the skin which you can work out by weighing a few banana skins.
Another thing worth considering is the fibre. This is often included in the carb values online. However, fibre passes straight through and is not digested.
The URL I quoted above uses 21g for carbs and 2g for fibre. I don't think it is a great surprise that these values add to the same number that you have quoted above (23g)
For example, if you decide a typical banana skin weighs 50g (this is a number I plucked out of thin air and have not measured it), for a 150g banana and we use 21g for the carbs per 100g
Therefore, carbs in your banana are (150-50)*21/100 = 21g
Using 23g carbs, ignoring fibre and including the weight of the skin, you would have calculated 34.5g.
This additional 13.5g carbs that have been calculated may explain the hypos. Although don't forget the 50g for the skin was a guess.
The other thing to consider is the time of day and whether your carb ratio is appropriate: do you often hypo regardless of what you eat at that time of the day?
Or whether your basal dose is too high?
Or if you are eating the banana as a post exercise top-up, you may find the hypo is caused by your exercise.
There are multiple things to consider.
