I agree with all of the above. He's eating and pooping. That's fantastic!!! YAY Artie!!
Virtually all drugs (including herbs) have "side effects." It only means that they don't do just one thing.
In humans, it has been noted that one "side effect" of Metformin (a diabetes medication) seems to be longer life, more so than can be accounted for by simply controlling diabetes. They are now investigating Metformin as a possible longevity drug for people who aren't diabetic. (Not all side effects are bad things.) Marijuana is used as a recreational drug, but it also has the notorious side effect of giving users "the munchies." Valium also has this side effect in cats, though it's more limited than the marijuana side effect in humans.
I don't know what the mechanism is that the motility drugs use; that might give you a clue to why they cause constipation, or it might not.
Artie has at least as much cause to feel exhausted as you do; I seriously doubt that it's anything to worry about. If he's eating, and pooping normally () the sleep is probably doing him a lot of good, as are the eating and pooping. Normal pooping probably means that he's also properly absorbing the nutrition from the food, which is exactly what he should be doing.
It's going to take both you and Artie time to recover from the trauma of excessive drugs while working out what actually works for him. And that trauma may well recur as Artie's illness changes with age. But I now believe that Artie will have the time to age. It won't be easy for either of you, but it will be worth doing.
Margret
He's eating well, and he's pooping ok. He's allowed to be more tired some days! You'll both be exhausted after the week you've had. Mega 
that today is a good day for both of you 
Fantastic news for the start of the new year - jumping for joy!
His tummy went through a lot with the loose stool. I would imagine like a person, it may take a day or two to bounce back.
I agree. I know it's hard, but try not to get too worried just yet.
