Ask HN: How do you stop being a toxic employee?

I've seen it happen. For whatever reason, an employee starts to get frustrated. Fatigue, burnout, mounting responsibilities, etc. They start to become visibly discontent, turning down happy hours, pushing back hard on anything not within the scope of their job, maybe even dropping off-the-cuff remarks about other employees or managers. This type of negative attitude feeds upon itself as they look at the world through shit-colored glasses.

Have you ever been here and successfully lifted out of it? How do you stop the burning and begin to heal? Without quitting or being fired. How do you repair your relationships with other co-workers at the organization?