Doctor Answers (2) on Pyschoneural depression
Kindly consult with your Psychiatrist at the earliest and discuss the excessive sedation that your father is experiencing. There are always options of non-sedating anti-depressants.
Secondly, with your father's cardiac history, it is imperative that he is treated aggressively for his depression as well. Evidence suggests that cardicac mortality increases with inadequately treated depression. So do not stop his meds at any cost.
Discuss this issue with your Psychiatrist in person.