A quick Google search would provide you a wealth of information on the subject, but in general:What's the difference between primary and secondary depression?
This must have been dreadful. My mother-in-law had dementia and passed away last year. Her's was not classic Alzheimer's but anxiety and depression which is really common among the elderly. We looked after her at our place for a while but eventually she asked to go to a nursing home where there was 24/7 support. Fortunately the facility where she wanted to go was only about a mile from our house.My stresses were due to being my mother's primary caregiver while she slowly sank into the depths of Alzheimer's Disease. I was alone at that time because my father had already passed and I have no siblings.