What do you tell your wife when she wakes up afraid and doesn't know why she is there and who you are?

This may be simplistic, but I've found that singing calmed my grandfather, especially when I sang songs from his youth. Sometimes, I could get him to sing with me, even when he couldn't form rational sentences.

brianlk: This is so difficult for you and for her. Calmly speak to her with reassuring words that are truthful, i.e. "I am Brian, your husband, who loves you very much." She may question this because of her illness. All rationale has gone. As Grandma1954 has said, she may indeed be unsure that you are her husband. In all cases, show her love.

Perhaps you have pictures together that can be framed and set in place around the house and on your phone?

Your wife is at the point in her disease where she's gone back in time to an age when she wasn't married to you, most likely. So she is looking for the people who she was sharing her life with at that time, when she was say, 20 years old. That's why she doesn't know who you are, and why she doesn't recognize your house. This is not an orderly time reversal; she may remember more or less on different days and at different times during the day. Early mornings & late afternoons (Sundowning) are usually the most difficult for dementia sufferers. Don't try to correct her, just take Grandma1954's advice and keep her calm, to the best of your ability.

I suggest you read this 33 page booklet (a free download) which has THE best information ever about managing dementia and what to expect with an elder who's been diagnosed with it.

Understanding the Dementia Experience, by Jennifer Ghent-Fuller 
https://www.smashwords.com/books/view/210580

Jennifer is a nurse who worked for many years as an educator and counsellor for people with dementia and their families, as well as others in caring roles. She addresses the emotional and grief issues in the contexts in which they arise for families living with dementia. The reviews for her books are phenomenal b/c they are written in plain English & very easy to read/understand. Her writings have been VERY helpful for me.

The full copy of her book is available here:
https://www.amazon.com/Thoughtful-Dementia-Care-Understanding-Experience/dp/B09WN439CC/ref=sr_1_2?crid=2E7WWE9X5UFXR&keywords=jennifer+ghent+fuller+books&qid=1657468364&sprefix=jennifer+ghent%2Caps%2C631&sr=8-2

She also has published a workbook entitled, “It Isn’t Common Sense: Interacting with People Who Have Memory Loss Due to Dementia.”

https://www.amazon.com/Isnt-Common-Sense-Interacting-Dementia/dp/1481995995/ref=sr_1_4?crid=2E7WWE9X5UFXR&keywords=jennifer+ghent+fuller+books&qid=1657468655&sprefix=jennifer+ghent%2Caps%2C631&sr=8-4

The 36 Hour Day is another excellent reference type of book you may want to pick up; it will answer a lot of questions you have on a daily basis about dementia.
 

Here is a list of useful tips from her e-book I found to be excellent:

The “Dont's”
· Do not reason and argue
· Do not demand that they reason or problem-solve
· Do not demand that they remember
· Do not demand that they get their facts straight
· Do not correct their ideas or scold them
· Do not reorient them
· Do not think that they are being uncooperative on purpose
· Do not think that they really do remember, but are pretending not to
· Do not use a “bossy” dictatorial attitude in care
· Do not act with impatience

The Do's
· Enter into their frame of reality, or their 'world'
· Be aware of their mood or state of mind
· Use few words and simple phrases
· OR use no words, just friendly gestures and simple motions
· Do everything slowly
· Approach from the front
· Wait for a slow response
· Constantly reassure them that everything is 'OK'
· Keep people with dementia comfortable 'in the moment' - every moment
· Maximize use of remaining abilities
· Limit TV or radio programs which they may feel are frighteningly real
· Maintain privacy
· Provide a safe physical environment

Language Needs
· Use short words
· Use clear and simple sentences
· Speak slowly and calmly
· Questions should ask for a “yes” or “no” answer
· Talk about one thing at a time
· Talk about concrete things; not abstract ideas
· Use common phrases
· Always say what you are doing
· If they repeat their question, repeat your answer as you did the first time · Give them a longer time to process information
· Wait patiently for a response
· Be accepting of inappropriate answers and nonsense words
· Speak softly, soothingly and gently

Best of luck to you.

Reassure her she is safe.
Gently remind her who you are. Just say "I'm brianlk, you are safe here at home"
If she does not "know" who you are and wants to know where "brianlk" is tell her that you will stay with her until he gets back. Don't try to convince her that you are her husband. Sometimes leaving the room one way and returning to the room from a different door will help.
Sometimes when I would be shopping with my Husband and he would start looking around I would ask what was wrong and he would say "I'm looking for my wife" and I would say "well can I walk with you until we find her" and I would leave the cart and make our way to the car and once he would see the car he would be alright.
If there is a blanket or toy that she likes hand that to her it will help calm her.
The sometimes difficult thing to remember is to not argue with her reality, you will never win an argument with someone with dementia it will just upset and frustrate both of you.