I'd advise to start on something slow and easy, like a default-style map.
I was in the state that you're in currently in. Losing motivation and various other emotions. Had an idea of a map in my head for as long as I can remember. You can check inf_Seed for reference, it was the map. Until two days ago I sat down on my PC to play Soldat and thought to myself- "You know what, I got this idea and I need to finish it and get it the fuck out of the way so I won't have to think of it again". And I did. After that, I pretty much got out of the slum I was in and now I'm back on track to make more maps like a machine.
If that doesn't work, then I had forced myself in the past. I sat down at my station and started mapping away until I made enough maps to keep me going. I forgot which maps these were, but they were recent. This seems to work more often than my above option. Try either and see if they work, they did for me.
