I am the mother of a recoverying heroin addict, before the H, he used oxys and before that perks.
when he was not "nodding" he was very hyper, talked alot, usually about really really stupid stuff. If he was on the computer or watching tv he looked like a zombie staring at the screen with his mouth open. it was kind of like day dreaming. His pupils were tiny but that depended on how long ago he took it, (the heroin) on perks his pupils were always tiny.
now that all of that is said, you need to stop looking for all these signs unless finding out is going to help YOU, not him because you cannot help him only he can do that.
you need to look out for yourself
good luck