Things like a UTI or other infection can cause a change in mental status. You might check it out. Otherwise, progression varies. My cousin had vascular dementia and the progression was rapid in a stepped down fashion. My dad had Alzheimer’s and it was quite slow with a gradual progression over the years.

Short term memory loss can be frustrating for everyone. It can be extremely stressful to have someone ask the same question over and over for hours with no memory they asked it 5 minutes previously. As a caregiver the only option is to nicely respond as if it’s the first time it’s been asked. Redirecting or changing the subject sometimes helps.

I hope your head is ok. Good luck with everything.