Be Yourself
So hard to say, because everyone is different. I can suggest doing the one thing you love the most, or confiding in the person you trust most.
Do something that engages you with the world. Volunteer. Exercise. Join a group.
But I would also say to take it slow. You wouldn’t run a marathon without working your way up (Sorry, I like running metaphors :P). So don’t try to spring back all at once, or you might burn out all over, again. This ain’t the movies.
Be good to yourself, and don’t beat yourself up about being down. Happens to everyone. Talk about it. Write about it. Rant and have a breakdown if you want. Whatever it takes to work through it.
There’s this whole cult of positivity out there, and it can make someone feel guilty about having any bad feelings at all. Like there’s something wrong with them. I say don’t listen to that. Listen to your own body and feelings.
Hope this helps. Sending good vibes. ^_^