Can the opposite happen to real meds? Like you think it won't work so it doesn't work?
Kindof. The meds will have their impact regardless but you can convince yourself that they're not working and they end up not working (effectively they work on the condition but you suppress the meds by over powering them)
It's the old saying of "Died of a broken heart". Studies found that stress, anger, depression, etc, can all lead to lowering the immune system and weakening vital organs. This is also why they talk about people "Fighting" when it comes to something like cancer. If you give up your immune system lowers and your organs slowly shut down, but if you keep up the spirits and keep fighting then you have a greater chance of survival.
Whether you're fighting because of God, or because of your family, or because you think the pills you are taking are doing something. The important thing is that you are fighting and you have a reason to believe that you can and must win.