Strange cat behavior...?

My cat disappeared about a week and half to two weeks ago. She just now got back but her attitude has somehow changed. I know she's my cat because of her eyes. Her attitude toward and growling at other animals is normal to me but she was also growling at me and she seems like she is in pain. I plan on taking her to the vet tomorrow to get her checked out. Is it normal for a cat to disappear only to reappear later with a different attitude. She acts like she knows us and doesn't know us at the same time. Is this normal or what could have happened to her?