My mom has Dementia and sometimes she wreaks havoc with her fits and hollering but later on she acts like nothing happened?

Sounds completely normal for someone with dementia. It can be kind of a roller coaster, up and down. Sometimes they seem totally out of it, other times seem quite normal. You just never know what to expect and just have to roll with the punches and deal with the behavior as it comes along.

That would be because she doesn't remember it. That's part of dementia. Educating yourself on dementia/Alzheimer's is your best bet to trying to understand why your mom does what she does. Her brain is broken, and it will never get better, only worse. Teepa Snow also has some great videos on this subject as well.