So here goes my magnum opus!
The normal numbers for blood sugar for cat is 50-100 mg/dl on a human meter. A cat is considered in remission when it's BG stays in the normal range without insulin for 2 weeks. While 100-120 is a just a little higher than normal, for a strong remission, you want numbers to be below 100 before you stop insulin.
The onset of Lantus is typically between +1 and +3 and then nadir between +4 and +6. We ask people to try and figure out (with tests) what their cat's behaviour on Lantus is - onset, nadir etc
Lantus is dosed twice a day with 12 hours between shots. You want to fix your shot time such that you can test till +2 wihout staying up late and on occasion (when the numbers dip lower) till +4 or even +6. If you shoot at 11am/11pm, you may be up most nights testing! Like I said earlier, most people shoot between 5am/pm and 8am/pm depending on their work schedules and whether they are night owls or early birds.
Lantus is a depot insulin and the depot take a few days to build and to empty. The 2U depot from giving shots twice a day could have affected his number for 3 days after you stopped. However, considering that he hasn't had insulin since the AM of 9/5, it is safe to say that his current numbers are not due to insulin or temporary. His numbers have come down due to a combination of a change to a low carb diet and possibly insulin for a month. It looks like he does need some more insulin support to get him into normal numbers (below 100) but we don't know how much.
The reason that diabetic cats feels lethargic/low energy when they first encounter lower numbers is because their bodies have gotten used to the higher numbers and normal numbers feel low - like a caffeine/sugar withdrawal. As they get used to lower/normal numbers they love them and start feeling crappy in higher numbers.
Both. His numbers are good enough that he won't suffer from another night without insulin and like I said earlier, you want to shoot at a time when you can get test up to as last as 4-5 hours after the shot without being up all night. Unless you are the kind who can nap between tests!
If you see this message earlier, I would suggest you shoot earlier so you are not up every night testing till atleast 1am. But if that works for you, it works for us!
If you could tell me what issues, I could you point you in that direction or connect you to someone here who can help.