I don't use social media per se. I have no Facebook, Instagram, Twitter, Linkedin, Tiktok, etc. These things are why you all have issues. "OMG, no one liked my post, so no one likes me." Asinine.
Sometimes, I don't feel like myself, that's life. When I feel that way, I know it's only temporary. I know I am the same great person and I am just having a mood. Maybe it's stress, maybe I made a bad decision, maybe I am dehydrated. What I don't do is try to figure out why, I just accept it is what it is.
But, maybe I'll have a drink or five, smoke a bowl or two, kill a kitten (or two) or take a nap. When I was young and not lazy, I'd hit the gym.
What I didn't do was let moods define me. Recognize things for what they are and deal accordingly.
Granted, losing your sister is horrible and not something you will ever get over. No one expects things to go back to what they were before. But I am sure your sister wouldn't want this loss to wreck you.
(Here's where all you chemical imbalance buffoons come in)