Why is my mom like this?

So, for context, I'm 20 and live with my parents.

Today I had a big fight with my mom about something, and I went out to the shop.

When I came back, she wouldn't let me home, she shut the door in my face and said that she is too angry at the moment and doesn't want me near her. I knocked a few more times, and since she hadn't opened, I went out.

I called my dad and told him everything, he said he would call her right away, and then both he and her kept calling me, begging me to get back at the house, that "mommy was just angry and went too far because I made her mad" .

Is this normal behaviour? I was so hurt, I was crying when I realised she slam the door in my face, of my our own family home, and later she begged me to come back, excusing her behaviour with "I was angry" ? Do you think a mentally stable mom would do this kind of thing?

Why is my mom like this?
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