I use facebook and i am always stressed. Might be the reason i use it for which is to help animals as i have a local animal rescue group. The stress is always there to find them a home, waiting on messages, posts etc.
I think social media itself is stressful to some people. Some of them think different from us. Putting yourself out there & info online , scruitinity of posting stuff , being reminded contantly bombarded by notifications and messages etc. All these things get people anxious and stressed about