My kittens had their 9 week shots today and the vet sent me home with some doses of Panacur. I'm to give each of them 1/4 of the sachet each day for 3 days. Well, they had their first dose about 4 hours ago and now seem really lethargic. They do sleep quite a lot being kittens, but they are quite a bit more tired than usual. Is this a normal side effect?