Why is this happening with my pedals/sprocket? How do I fix this?

I recently was having chain tension issues with my bicycle. I took it into a bicycle shop for a service and it felt great for a day or two but now this is happening.

[https://www.youtube.com/watch?v=sDhhOeHbTt8](https://www.youtube.com/watch?v=sDhhOeHbTt8)

What do I do?

by JayWelsh