My doggy used to lose a few lbs. every summer when I went to visit my extended family.

Since she was always a little chubby, that was a good thing. But of course, soon after my return, she would bounce right back!!

This is normal, OP. This isn't really a "depression" but she's just missing you and reacting to your absence. I would say 90% of dogs react this way to their owner's absence. If she didn't do it, it would be abnormal.

You are a good owner to worry, and have someone stay with her. She's fine.

I have a six year old jack who often goes into a depression when I go away on vacation for more then two days. I feel so horrible about leaving her but I can't take her with me every time. Even when I leave her at home with my brother looking after her, she still only eats a little and is less active. My brother sleeps over so she has someone familiar to cuddle with. I'm not a crazy dog person who treats her like a child, she's a dog and treated as such but I worry about what a long extended vacation will do to her health. When I return home she usually bounces back to her normal self immediately and after greeting me starts to eat every last piece of food she left in her bowl.

How should I handle my next vacation?

( I can't get a Companion dog but i do have two cats that have grown up with her)