This is a question looking for subjective answers but a common one, so I'll give it a go.
I know exactly how the above feels and I think it's a motivation issue. To address it I find that I need to things to get going again:
- A relatively simple task/job that has a clear requirement(s)/goal(s). It's something that I can complete in a day or less. Even better if it's a milestone/part of a bigger more complex project.
- The above task/job must be enjoyable and immersive. It's something that you can get stuck into for a hours and get going without needing much push. For myself personally, this could be something involving programming/making things. Like an early mock up/prototype for a project or something like that.
When I get into a task that fits above and complete it to requirement and on time (that I or someone/something set for it externally) I'm back in the game. It gives a confidence boost as well as energy and focus needed to get on with bigger things.
Important note: I don't think it's too hard to find a task fitting the two criteria. It can even be vaguely related to the bigger jobs you have to get done. Sometimes even errands/house jobs and projects you have been putting off could work. As long as it gives you a sense of accomplishment in the end it should work because you are bound to want to get that feeling again, soon and in bigger quantity which will require you to do something bigger, more complex and more meaningful, ultimately getting you into the groove.
As I said at the start, this answer is subjective in line with the question posed. We might get a completely different answer below which would fit your preference better.