This is a link to an article on the BBC website about Alzheimer's being a form of "brain diabetes".
http://news.bbc.co.uk/1/hi/health/7866022.stm
Firstly, I have to say I am not medically qualified, however, I have some knowledge about dementia care and neurological illness.
Most causes of forgetfulness are probably not an organic brain problem. People who are either stressed or anxious or depressed, or any combination of those things tend to forget things. You tend to forget more as you get older, simply because you know more things to forget.
Forgetfulness can also be due to any number of physical illnesses, including brain injury, thyroid problems, vitamin deficiency or being anaemic. Also, things such as respiratory tract infections and urinary infections can cause something known as "acute confusional state", this is a confusioanl state whioch cones on very quickly and respinds to treatment with antibiiotics. As Dennis said, this is also one of the symptoms of hypoglycemia. Forgetfulness can also be related to medication side effects. It can also be related to long term heavy alcohol use.
Research has shown that there are many factors which increase the risk of someone developing progressive memory problems - including Alzheimer's - and these include general anasthetics, heart conditions and diabetes.
However, just because you have one of these risk factors does not mean you go on to develop a dementia. Just as not all overweight people will go on to develop diabetes. If you are under 65 it is much more likely that you have a problem that will respond to treatment. If you are worried you should talk to your doctor.
The Alzheimers Society has some excellent information and advice about memory problems on this page
http://www.alzheimers.org.uk/site/scripts/documents.php?categoryID=200137 Their fact sheets also include information about memory problems not caused by dementia.
Diana Friel Mcgowan, author of "Living in the labyrinth", the book she wrote about being diagnosed with Alzheimer's at a young age, said that everyone loses their house keys, but if you have lost the house, that is a problem.