The problem with testing your blood sugar while having a seizure (or immediately after) is that seizures, as with other stresses to the body -- such as illness -- will raise your blood sugar.
Our son is on the ketogenic diet, and part of the regimen is to test his blod sugar at least once a day -- and yes, you're right, blood sugar does have a marked effect on seizures. Our son has good seizure control when his blood sugar is in the 60's and 70's -- when it gets into the 80's or higher we start seeing seizures. But...also...seizure have an effect (temporary) on blood sugar...so I suggest that if you typically have seizures at night that you test your blood sugar prior to going to bed each night -- to get a better reading, it's best to wait 2 hours after you eat.
You might also want to check your blood sugar upon awakening in the morning, prior to eating anything. Then you can establish a sort of a pattern -- first, you'll find what your typical blood sugar is, and whether you're having any issues with elevated blood sugar (over 100). Secondly, you'll discover whether an elevated blood sugar level at bedtime leads to a seizure. If you do find a relationship between the two, you'd want to reduce your carbs and high glycemic foods (esp. sugar, and white bread, rice, etc.) and maybe even start an Atkins like diet.
Blood sugar testing kits can be purchased over the counter, and you can consult with your local pharmacist as to which ones are easiest to use.
The two that we use are Freestyle Lite and Accucheck. I like Freestyle Lite better because the stick is easy to use and the puncture wound is smaller (it doesn't take as much blood) and it's easy to pop it into the test meter. The downside is that the test strips are really expensive. Accucheck is cheaper, but more cumbersome to use -- I find it really awkward.