When a cat's body has gotten used to high numbers, some of them do feel wiped out when their blood sugar drops. I think of it as like caffeine - your natural state is uncaffeinated, but if you're used to it and then it gets taken away, you feel awfully wiped out.
think of the insulin as being somewhat timed release. Some of what you've been injecting in the past 3 days is still lingering in his body and will continue to release even if you skip the shot. When you shoot, some goes immediately to be available to the body and some forms a precipitate in the body and slow releases.
Reducing the dose, like BJM suggested doing a one-time 2.0u shot tonight, can be enough to prevent low numbers, but it's hard to say for sure. So you still would want to check in another little while. Skipping the shot is more likely to prevent the low numbers tonight.