I have seen people who get poonakam also called convulsion in medical terminology. This is usually seen during festivals of Grama Devatas in villages where the Devata manifests in ordinary people. What I observed from those instances is that those people are either from poor families or stress minded or those who are facing too much difficulties in the society. I want to know whether this is real or a type of psychological disorder that arises due to the feeling of insecurity?
There may be numerous reasons behind the poonakam.
It can be psychological excitement for his favorite god. It can be due to transmission of energy from the deity to the devotee. It can be result of yogic energized charkas.
If one can not completely with hold this energy/excitement/joy received, it may over flow and exhibit as poonakam. This manifestation can be real or can be just excitement or can be a bluff public stunt. If god has really come to one's body, then he would experience oneness and experience the tranquility.
When in hardships people generally pray more and be devoted more and hence your observation may be true to some extent. I knew many people who are secure enough (economically, physically & mentally) but still get poonakam.