Depression Forum - Alzheimer's disease or depression ?

Allright guys, once again i need some advice this time it is my dad. He's 51 years old turning 52. This girl he's been seeing dateing or whatever it is, has been going on for about 8 yrs, they have been married a few times, gotten a divorce a few times. And by the way she is a heavy drinker. She'll come around tax time to take his money and leave again. Does this all the time, and my dad takes her back. Anyways for the past few months, he's been acting like he's depressed. Not wanting to do anything, sits in the house, like yesterday he started a new job, cuz his factory was shutting down, so my boyfriend got him a job up where he worked. Well this morning my brother went over there to pick him up for work, and he just started crying. He couldn't handle the work. And the work was so easy, compared to what he was doing before, and he just couldn't handle directions, like he couldn't rememeber what he was being told. And the other day, my brother in law called him to see what street he lived on, cuz my dad had his kids, and he didn't know what street it was he had to think about it, and he just broke down again. He's losing weight, can't remember anything.

And all of us kids, we just don't know what to do. He's a very stubborn man. He hasn't been to the doctors in years. And his girlfriend says he just seems like he's going down hill, fast. We were thinking maybe alzehiemer's disease, but then depression. ANy advice would be so appreciated. We are so worried about him, or if anyone knows how to approach him so he doesn't get pissed off at us or mad at us, cuz one thing i don't want to happen is he gets so mad at us for telling him, he just doesn't tell us anything and something happens to him and we wouldn't know i don't know, someone please write back