I don't just start feeling down but I get angry at the BS on FB. I have a neighbor who always does the "my life is so great!" spin on FB, but living in the same street we see more of the reality than maybe some other people. I can't be on FB because it would mean calling people like her out on their BS, she is ugly (sorry but she just is by anyone's standards), her children are awful spoiled bitches, her constant posts about how sporty she is are lies and all she really does is spend money on sports shop brand names she can't afford. It's a true lifestyle spin that really makes me dislike her and worse ... I dislike myself for feeling like I should care and for not speaking up. So I try to avoid the negativity and BS (I learn about this person through my SO who reads it out to me sometimes). The problem with FB as I see it, is that it doesn't bring people closer together but pushes them apart because instead of being involved in some dialogue, face to face, you are left to silently judge and be judged.
But if your town has a "buy, sell, give away" group you should join, those are great.
Clicking on their profile and downgrading from 'friend' to 'acquaintance' I find helps a lot. You then hardly see their stuff. I've had to do that for four annoying people (far right politics, topless pics, fascist propaganda etc...) and I don't think I've seen any of them in my feed since.
Tbh, I haven't been on FB since I abandoned my account in about 2010 so I'm unaware of these new features like "aquaintance", I thought everyone had the same status of friend. I'm more worried about FB tracking and privacy, I have banned my SO from opening FB on my computer, not that does much on a shared IP.
But if your town has a "buy, sell, give away" group you should join, those are great.