this is semi related, but back a few weeks ago, when l gave my dog heartworm meds from the doc, he did the same thing and sat and looked into space. in fact sometimes he even started swaying left and right from being too tired. I think its because they were never used to the changes in their body, therefore they are trying to get used to it, but tries to stay away from the owners because it might scare them (read that somewhere online, l forgot where)