Delusion could be caused by physical problems or chemical problems.
MRI test is needed.
If it is not physical cause, then it is chemical cause. the nerves communicate to each other using chemicals substances.
The sender nerves generate the chemical substances and the receptor nerves receive them. This is how they communicate. When there is illness, the sender generates too much chemical substances and the receptor receives too much. This is the cause of the non-real feeling.
The medicine can get absorbed by the receptors on the receptor surfaces. These medicine blocks some of the chemical substances so the receptor can be regulated to receive the right amount of the chemical substances to have the right feeling.
This is why it is very important that the medication needs to be managed by the Dr wrt dosage, choices and duration.