If you are dehydrated (easily done in this weather) and your blood sugars are low (quite possible when followind a dietary regime) then it is entirely possible that you will experience a lack in concentration. Changing hormones can also be a factor and I would hazard a guess that it is multi-factorial.
You're a little bit young for dementia, but just monitor the situation. If you got lost whilst driving home or suddenly thought about paying a visit to an aunt who died a few years ago, that's the time to worry :)