Dealing with setbacks

After the hardest summer of my life, I slowly regained power over my thoughts and started to feel happy again. Although, I had some minor setbacks along the way, I still was able to recover even more! Two days ago, I had, yet again, another major setback. I feel so powerless. It feels like, everything I achieved is drifting away. The hard work to defy rumination is gone and I feel like I was having a blackout where I cannot recall how to deal with rumination/intrusive thoughts. Any tips?