My mother has so many mood swings for what seems to be for no reason at all?

It started about a year ago, but something I want to highlight is something that happened today. I was just sitting with my mother and showing her through something I wanted to order (because I needed her credit card details) and then suddenly she told me to just get out of the room. I don't know why, but she raised her voice and just got angry. I listened to her but I'm just so angry that she has to do this! She makes a big deal out of tiny things. It's a bit annoying, but why is she acting like this? She's smarter than this

Thanks for your help