if you had worked up to the 5 unit dose slowly according to protocol, then yes, dose reductions would be done slowly. In that case, we usually reduce by 0.25 units at a time. We can do that because of the way we work up to the dose (also by 0.25 units at a time, and only after a lot of testing). By working up to a dose that way, we know the dose is safe. For example, if Boots had worked up to 4.75 units and was still getting high numbers, we would know that 4.75 wasn't enough, so it was safe to increase to 5 units.
However, without the data to back up those dose increases, we have no way of knowing if 5 units is safe for Boots. We're thinking that it is probably not - after dropping to 80 at +3 last night, and waking up even lower than that, Boots could have gone much, much lower than 80 last night. The fact that his bounce is as high as it is means that he probably did go quite a bit lower. We don't know how low. We do know that a dose that is too high, causing numbers to remain in the 40's 14 hours later, can be very dangerous. His liver can protect him for a while, but you can't count on it to do so every single time. Probably something very similar happened overnight on the 9th to cause his bounce to the 500's.
Numbers that are too low can kill instantly. Numbers that are too high can cause him to be uncomfortable, and over time can cause problems, but in the short term it's much safer to be too high than too low.