It seems like mom was having a psychotic episode, thinking I had abandoned her! Is this common with AD patients?

Yes, have her checked for a UTI at her doctor's office and report her behavior to the doctor. Any new behavior should be reported. Perhaps her doctor can prescribe medication if this behavior becomes normal for your mom.

As you know, Alzheimer's is progressive. This may become the norm if it's not a UTI. I hope you find some answers.

Have her checked for a UTI and let her doctor know of the behavior change

Some folks at mom's memory care do have fits when they're upset

Mom has had AD for about 8 years. She is legally blind and 96 years old. This happened about an hour after putting her to bed for the night, but has never had this happen before. She was literally freaking out, digging at her scalp with both hands, crying and shaking terribly! What is happening here? I am terribly afraid to see this again!

Could you give a little more background so we can give you more thorough answers?
- was your mom diagnosed with AD?
- what are your mom's health issues?
- when did this occur? Nighttime? Day time?
- has your mom had these episodes before?