Thank-you, all of you, for your replies, thoughts, and prayers.
Pepe made it through the last 24 hours without anything but maybe the second symptom listed here:
http://www.felinediabetes.com/hypogly.htm
It is kind of hard to judge lethargy in a cat.
He was really active the first 9 hours after I dosed him with me playing with him and giving him extra treats.
He is mostly an indoor cat but he jumps on top of a bar-stool to have his harness put on to go outside with his 16 foot retractable leash
tethered to a milk crate so he cant get to far and also I can put him in it and carry him if a stray dog comes around.
He almost caught 2 ground squirrels yesterday.
When he finally went down to rest after all the extra exercise and treats (pizza crust and milk from the bottom of bowls of Honey Nut Cherrios)
My wife and I kept an eye on him to make sure he was OK.
I know this forum is home testing-centric and I have just been following the vets prescription
of 5 units twice a day for the last 3 years without doing that but I am so glad that this place is here
and that the above link and some other info helped me through my awful mistake.
I plan to change some default behaviors in my needle count/journal of times but mostly in the extra dose
kept in the refrigerator for the few times I am not here to administer the dose.
Refilling the dose is how I sleepily/absent mindlessly double dosed him yesterday.
From now on I will refill the dose as soon as possible and not wait until the next time I am to give Pepe his shot.