I have a 10-year-old labrador retriever who has been acting "odd" this past year. She used to be very excited when people came to the house, she loved to play (although, in smaller bursts as she's gotten older) and she'd devour anything in sight. One of the best pets I've ever had. Now she's very listless and it's not uncommon for her to not finish eating her dinner until the following morning (it's the only meal she gets routinely fed) - plus, she no longer will eat table scraps or human food (she will still eat chicken, though). She seems very depressed.
My family has spent a small fortune trying to diagnose her, but nothing has popped up save for some elevated liver count numbers. We'd have to do a MRI to find anything else and we just don't have money to burn.
Today, she spent most of her time on the second floor - a rare sight these days - and threw up four times. Then she collapsed on the landing and began to pant. She would not move. It took three people, myself included, about thirty minutes to get her to stand and come down to the first floor, where it's much cooler and she has access to food/water. She's also been drinking a ton.
I've had other dogs before and this behavior seems pretty scary.