As Simon says
Like all the demon-possessed people in the bible, they were ( all ) suffering from mental illness.
And I totally agree with that statement.
I knew of a couple of sisters in different congregations that claimed the Demons were having sex with them ..?
The demons if they existed at all are spiritual not physical so how could they have sex with a human ? According to the Bible that privilege (?) was taken away from them at the time of the flood so that they couldn`t produce hybrids such as the Nephilim any more.
it`s all in the mind that can play weird tricks on us when we are vulnerable
The bottom line is do not be afraid of Demon possession it ain`t gonna happen.