How can we convince Mom to see a doctor?

Hello, my name is Tom and I'm sixteen. My mom has been sick for a couple of years.Both me and my dad know that there's something seriously wrong with her but she always denies it and refuses to go to a doctor. Both her parents were dead even before she met my dad and we don't think she has any living relatives that we can ask.

She's in bed almost 24 hours a day. We bring her food and she goes to the bathroom. The rest of the day she sleeps or just lies in her bed. Her room is always dark and she hates it when the light is on. Sometimes when she wakes up she doesn't remember who we are and she panics. Sometimes when her memory is 'fuzzy' (as she calls it) she gets really aggressive and my dad has to hold her down.

We first thought it could be dementia but she's normal sometimes and we also found something called Pick's disease... Could this be it?

Please help us.