Depends how severe and pervasive it.
Don’t isolate. Even if what you’re doing is isolating, find a way to connect with others and life. Find someone you can check in with regularly. Find time to get outside and move your body even if for a moment each day.
A lot of the best wisdom I’ve gotten from books are form Eckhart Tolle’s work. I highly recommend “the power of now”.
Happiness comes from within. It’s not, “when I get to this stage in life or reach this goal, I will be happy” or comparing yourself to others/where you should be. You already have everything you need to be happy, you just have to seek it.
I’ve been there and I’m here for you, truly🫂