It’s called depression and when it happens because of a situation in your life that you have limited control over it can be very difficult to recover. Get professional help if you haven’t. It is hard. Been there.
Time. Focused effort. For me my happiness set point is decent. It takes work to get out of the hole though. No one thing. Exercise. Diet. Forcing myself to do things I know I enjoy. It can feel hollow, but it comes back. Lots of meditation, stoicism, cognitive behavioral therapy. Recognize the negative thought pattern loops early, combatting them, reminding yourself what they are.
