Mom just passed and dad seems to have sudden onset dementia. Is this normal?

As Wally said, sometimes the spouse "covers up" for the person who has dementia so well that the rest of the family does not realize just how "severe/bad" that person is until the spouse goes into a nursing home or dies.

This happened with my sister-in-law's parents.  It wasn't until SIL's Dad went into the nursing home that the children realized just how severe their Mom's Dementia was.  SIL's Mom had to go to a Memory Care Unit at the same nursing home that her husband was in.

My Mom has relived my Dad's heart attack that occurred in their townhouse at supper time in 2007 and she cries and gets upset every time.  (They had to "scoop Dad up" and do CPR on the way to ER and in ER Dept.  I was the one that told the doctor to stop all treatment and Dad died 30 minutes later.)

In 2017, my Mom's younger brother (age 84) died in March and her older sister (age 91) died in April.  We were not able to go to either funeral.  The funeral for Mom's sister was scheduled the same day that we were out of state for Mom's grandson's wedding.  It took 5 hours to drive home the day after the wedding.  30 minutes after we got home Mom said that she needed to go to ER Dept. b/c "her back hurt".  She was admitted to the hospital 1 week after her sister died and within 48 hours Mom went from being able to take care of herself--do own ADLs, walk, talk, etc. and changed to-- NOT being able or not wanting to eat, talk, walk, do own ADLs, and she was incontinent.  Mom was transferred to the nursing home for Rehab Therapy but she fought the therapists (after her Total Knee Replacement in 2013 Mom LOVED the therapists and loved doing the Rehab Therapy).  The Psychiatric Nurse Practitioner diagnosed Mom as having Mild Dementia (which I think worsened after both of Mom's siblings died leaving her the only surviving sibling)and Major Depression with Delusions.  {Also, several of Mom's friends died in 2016 and 2017 which resulted in 2 social groups that Mom was involved in to dissolve as there were only 2-3 members left.} 

So, yes, I think that it is quite possible that the stress of losing his "life partner" has affected your Dad and made his Dementia worse or appear worse.  He might get better as time goes by or he might get worse...it just depends.  Let your Dad grieve the loss of his wife and soul mate and maybe his memory will get better as he grieves.

My dads level of dementia was fairly advanced when mom died a few months ago. He had little short term memory. He couldn’t remember what happened and was reliving the grief each time it was explained.

Very soon we starting fibbing and diverting. Mom’s in rehab...Fell and in hospital.....He was used to these events and would accept it and stay calm.

He now thinks a lady in his memory care unit is mom. Staff rolls with it. Sits them together at meals. Whatever works...

if you have been spending more time with him than normal, it may be that you are just noticing more (?) my mom and dad were always able to cover-up or hide their dementia. but when I spent the day and night with my dad. that's when I totally saw how *bad* he was.(and how dementia affected everything) and my mom was complaining a little about my dads behavior but not too much. and she ended up to be almost as bad as he was.

but im sure the stress of losing wife probably makes it worse.

It's possible that the stress of bereavement, affecting all of you, had a physical/physiological impact on your father - do you have any way of checking his AFib episodes?

I'd discuss this with his doctor, but at the same time keep in mind that you must all still be terribly upset so soon after your mother's passing and so be open to giving him a little time to adjust. As your father settles he may regain some clarity, but then again how can it hurt to take medical advice?

I'm so sorry for your loss, and the distress you're all undergoing.

Stress of any type increases dementia symptoms. Group gatherings, change of living environment, change of routine, etc. Sounds to me like your dad has some mild dementia (probably vascular) from the stroke but he was coping well with his wife's assistance. Now he has had too many changes too quickly to cope. His mental state will likely improve some in the coming weeks but he may still not be able to take care of himself with some support.

Short term memory loss alone doesn't impact daily living in major ways as long as there is a routine and someone around to provide/enforce the normal structure. My mother's short term memory is shot, and that means recent memory has major holes (long term memories are written from short term memory) but she follows all her normal routines for dressing, breakfast, taking medications, brushing teeth, applying moisturizers, reading newspaper, cleaning the kitchen, etc. very well. She could shop for groceries without problems until the store was rearranged, then she began struggling because items were no longer where she expected them to be. Mom doesn't have dementia, but finding things had "changed" that she had no memory of is upsetting. She still wants to be clean, take her medicine and daily walks, etc. She takes her medicine from a medicine box well (she can check the box to see if she has already taken it), but may not remember to eat lunch unless I actually fix something for her to eat and place a plate under a dome keeper. She is still capable of fixing that plate from leftovers in the fridge. If I leave a plate in the keeper, she reheats in the microwave and eats lunch consistently.

My father's vascular dementia (from multiple TIAs and a couple of small strokes) impacted memory, balance, and impaired his abilities to execute even long standing daily routines. He doesn't bath, change clothes, eat meals (although he snacks) without prompting and sometimes help too - perhaps the type of prompting your mother had been providing.

It's also possible that without your mother to monitor his food intake, his blood sugar is varying enough to impact his thinking too. The effect would be increased for someone with even mild dementia.

I am sorry for your loss of your dear mother. I was told by medical staff at my mother's nursing home that a sudden trauma can cause early beginnings of dementia. When my sister passed unexpectedly, we saw a change in my mother's behavior and personality.

So Sorry for your Loss!!
When my Dad passed at 91 years, after a 67year marriage, Mom was very understandably confused and distraught.  They both suffered dementia, though somewhat differently.  She was a full month or 2 getting back to anything close to normal!!  Give it some time and, hard as it is in your own grief, be as compassionate as possible.  All that your Dad sees is his own Loss!   those broken brains again!

We have found that stress, depression and lack of self care, especially not getting up and moving or drinking enough water, effected our Mom. One of the other things not mentioned above that seemed to help her was to spend time talking about pleasant memories in the past (long term memory was OK, short term was very affected) and to make plans for something fun to look forward to. I also notice a slip backwards in her memory when she is not drinking enough water.

Stress of caring for a cancer spouse, who then dies, can indeed produce temporary dementia.  When caring for my first husband, I occasionally got lost on a familiar route.  My fear was brain tumor, but my therapist laughed and explained stress.  However, after DH's death, I had some severe health issues pop up.  So, It could be either.  It needs to be checked out by a doctor.  I am sorry for your loss, and your dad's resulting grief and health.  Big hugs.

yes it is sounds like dementia I would suggest getting him evaluated . And document everything.