Mary, Mary, Quite Contrary - Multiple Entity Communication Attempts Leads to Possession

I find myself home alone (for once) so I take this opportunity to repeatedly try and communicate with the Entity until it responds.

Having reached over 20+ attempts, I start to fatigue and get a headache. As I get to attempt 28, I experience blinding headaches. After one of them, I find myself standing up, feeling overwhelmingly sad, confused, and having no recollection of standing voluntarily.

The tripod has been knocked over and the camera has been knocked out of the tripod.

As I watch back the footage on the camera, I see what really happened!

Who's Mary?