JERRYBANFIELD SUPERNATURAL WRITING CONTEST: Demon or Illness

This happened when I was about 5 years old, one thing I don't think I can ever forget. It happened to my elder sister Miriam, she was 11 at that time.
It was a Friday evening I think (some details are quite sketchy, its been so long ago), we were returning from school, we usually come back alone because our school was really close to our house, just down the street. We were playing with a stone, kicking it as we were walking, laughing and having our little fun (We were really really close), then we started hearing loud noise that seemed loud shouting coming from a nearby church, our curiosity got the better of us and we decided to go check what was going on. The noise became louder as we got closer, the weird thing was that it didn't sound like just praying, there was this other strange noise coming from inside, we got to the door and opened it and the sight was just so scary, people surrounded someone and were shouting prayers, and the person was screaming in response, some people turned back to look at us and we immediately ran away. We were so filled with the spirit of adventure that we kept talking about it all through the journey back home. When we got home we told my mom and I can remember her telling us not to do that again and we shouldn't even go near that church again, we asked her why and she told us to just listen to her. I think I dreamt of the event that night. The next day was a Saturday so we wake up not as early (surely). I went to my sister's room and she was still asleep, woke her up and she just opened her eyes and was staring at me, i remember feeling quite scared, don't know why but I just did, she didn't say anything for some seconds (which felt like ages), then i called her name and she sort of jumped up, like she was just waking up, i told her that her eyes were open earlier but she said I was lying, said she just woke up so I let it go. Fast forward to Sunday night, i woke up to go ease myself and she wasn't on her bed so I thought she was in the toilet, stayed back for sometime waiting for her to finish but she wasn't coming back, i got too pressed that i just went to the toilet, knocked and called her name but nobody answered so I opened the door ready for whatever she was going to say, but to my surprise, no-one was in the toilet. After I eased myself, i got back to the room and she still wasn't there, i decided to go check out what she was up to and I saw her in the sitting room, standing and staring at the television that was showing static, i called her name and she didn't reply, i got so scared I went to bang on my parents door, they came out and I took the to the sitting room, they touched her and called her name but she was just standing still and staring, and then she suddenly fell down. They started praying immediately (Nigerians are very religious people). They prayed for hours and called our pastor, who also prayed and told them he'll come first thing in the morning (all the while she was still asleep) when they were done, they carried her to the room and told me to sleep with them. The next morning, she woke up and couldn't not remember anything that happened the previous night. She didn't go to school but sadly I did. I was practically running back home after school and out pastor was there with my parents praying for her and anointing the whole house. They anointed me too and that was that. In the night I woke up and she wasn't on her bed once more, went to quickly call my parents and they rushed out, there she was again staring at the television and not moving, it was super scary now and my parents quickly called the pastor who drove down to our house that night, they prayed for hours until she fell down. They left her there for the night and my parents slept with her in the sitting room, our pastor went home. The next morning she woke up very aggressive, kept shouting when anyone wanted to touch her, breaking plates and cups, scratching my dad when he tried to restrain her, insulting everyone and threatening to kill us all, i was scared so scared. The neighbours came in and she kept calling them witches and saying she would kill them. Our pastor was called yet again and I heard him telling my parents "the demon jumped into her from that church that was casting out demons and it's beginning to manifest fully. They tied her up, stood around her and started praying and pouring her anointing oil. Then she started making some screeching sounds (Like the one we heard in the church) I got scared to my pants (if you know what i mean). They kept praying and praying until she finally calmed down and slept. One of the neighbours suggested taking her to the hospital and they refused, they said it was not a medicine matter, it was forces at play. When she woke up, she said kept saying she was hearing voices telling her to leave that house and the prayer continued, the pastor said "we are winning, the demon is not comfortable, he'll soon leave her" they kept praying and she became violent again. When she finally calmed down, another neighbour also suggested taking her to a hospital just to treat the injuries she acquired during the episode. My parents finally agreed and took her there. They left me at home. My mom got back later and said she was admitted but the Doctors said she was going to be fine. Some days later she came home with some medication that she took for awhile.
Now, I'm grown and in medical school and I've been taught that all that could be a psychotic episode of schizophrenia despite all we've been told about demon possessions. So I don't know, was it actually a possession by a supernatural being or just another medical condition that was treated? I just know that those screams are still in my head.