Mom has Parkinson's related dementia and woke up one day and didn't know me. Does this happen?

She has had a difficult year, in and out of hospitals. She had a TIA, UTI, pneumonia, another UTI. She's been home for a month and 1/2 and last week after I gave her a shower she didn't know who I was. She seemed ok after I re-orientated her but than this week didn't know me again. Since than she goes in and out of remember I'm her daughter to forgetting. When she does remember she thinks we were just reunited.

When it first happened I called the doctor and we got her a urinalysis. That came back clean. I was supposed to take her today to get blood work but she ended up getting very dizzy and vomiting. She's resting now. The doctor said if she has a hard time keeping liquids down to get her to the ER but if she can hold that down it's probably just viral.

I just wonder, can a dementia patient wake up one day and forget who her daughter is. The daughter who she's lived with for 38 years and has always taken care of her? It just feels so sudden. Just woke up one day and didn't know me.